diff --git a/hadoop-common-project/hadoop-common/src/main/bin/hadoop-daemon.sh b/hadoop-common-project/hadoop-common/src/main/bin/hadoop-daemon.sh
index 9d19250..3e5f20b 100755
--- a/hadoop-common-project/hadoop-common/src/main/bin/hadoop-daemon.sh
+++ b/hadoop-common-project/hadoop-common/src/main/bin/hadoop-daemon.sh
@@ -141,7 +141,7 @@
     echo starting $command, logging to $log
     cd "$HADOOP_PREFIX"
     case $command in
-      namenode|secondarynamenode|datanode|dfs|dfsadmin|fsck|balancer|zkfc)
+      namenode|secondarynamenode|datanode|journalnode|dfs|dfsadmin|fsck|balancer|zkfc)
         if [ -z "$HADOOP_HDFS_HOME" ]; then
           hdfsScript="$HADOOP_PREFIX"/bin/hdfs
         else
diff --git a/hadoop-common-project/hadoop-common/src/main/packages/templates/conf/hadoop-policy.xml b/hadoop-common-project/hadoop-common/src/main/packages/templates/conf/hadoop-policy.xml
index 131fecf..2c324cf 100644
--- a/hadoop-common-project/hadoop-common/src/main/packages/templates/conf/hadoop-policy.xml
+++ b/hadoop-common-project/hadoop-common/src/main/packages/templates/conf/hadoop-policy.xml
@@ -239,5 +239,12 @@
        group list is separated by a blank. For e.g. "alice,bob users,wheel".
        A special value of "*" means all users are allowed.</description>
     </property>
+  
+  <property>
+    <name>security.qjournal.service.protocol.acl</name>
+    <value>${HADOOP_HDFS_USER}</value>
+    <description>ACL for QJournalProtocol, used by the NN to communicate with
+    JNs when using the QuorumJournalManager for edit logs.</description>
+  </property>
 
 </configuration>
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/test/GenericTestUtils.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/test/GenericTestUtils.java
index 2a361d9..dd0c955 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/test/GenericTestUtils.java
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/test/GenericTestUtils.java
@@ -25,6 +25,7 @@
 import java.util.Set;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.regex.Pattern;
 
 import org.apache.commons.logging.Log;
@@ -48,6 +49,8 @@
  */
 public abstract class GenericTestUtils {
 
+  private static final AtomicInteger sequence = new AtomicInteger();
+
   /**
    * Extracts the name of the method where the invocation has happened
    * @return String name of the invoking method
@@ -55,6 +58,14 @@
   public static String getMethodName() {
     return Thread.currentThread().getStackTrace()[2].getMethodName();
   }
+
+  /**
+   * Generates a process-wide unique sequence number.
+   * @return an unique sequence number
+   */
+  public static int uniqueSequenceId() {
+    return sequence.incrementAndGet();
+  }
   
   /**
    * Assert that a given file exists.
diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.HDFS-3077.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.HDFS-3077.txt
new file mode 100644
index 0000000..46ea04d
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.HDFS-3077.txt
@@ -0,0 +1,88 @@
+Changes for HDFS-3077 branch.
+This will be merged into the main CHANGES.txt when the branch is merged.
+
+HDFS-3077. Quorum-based protocol for reading and writing edit logs. Contributed by Todd Lipcon based on initial work from Brandon Li and Hari Mankude.
+
+HDFS-3694. Fix getEditLogManifest to fetch httpPort if necessary (todd)
+
+HDFS-3692. Support purgeEditLogs() call to remotely purge logs on JNs (todd)
+
+HDFS-3693. JNStorage should read its storage info even before a writer becomes active (todd)
+
+HDFS-3725. Fix QJM startup when individual JNs have gaps (todd)
+
+HDFS-3741. Exhaustive failure injection test for skipped RPCs (todd)
+
+HDFS-3773. TestNNWithQJM fails after HDFS-3741. (atm)
+
+HDFS-3793. Implement genericized format() in QJM (todd)
+
+HDFS-3795. QJM: validate journal dir at startup (todd)
+
+HDFS-3798. Avoid throwing NPE when finalizeSegment() is called on invalid segment (todd)
+
+HDFS-3799. QJM: handle empty log segments during recovery (todd)
+
+HDFS-3797. QJM: add segment txid as a parameter to journal() RPC (todd)
+
+HDFS-3800. improvements to QJM fault testing (todd)
+
+HDFS-3823. QJM: TestQJMWithFaults fails occasionally because of missed setting of HTTP port. (todd and atm)
+
+HDFS-3826. QJM: Some trivial logging / exception text improvements. (todd and atm)
+
+HDFS-3839. QJM: hadoop-daemon.sh should be updated to accept "journalnode" (eli)
+
+HDFS-3845. Fixes for edge cases in QJM recovery protocol (todd)
+
+HDFS-3877. QJM: Provide defaults for dfs.journalnode.*address (eli)
+
+HDFS-3863. Track last "committed" txid in QJM (todd)
+
+HDFS-3869. Expose non-file journal manager details in web UI (todd)
+
+HDFS-3884. Journal format() should reset cached values (todd)
+
+HDFS-3870. Add metrics to JournalNode (todd)
+
+HDFS-3891. Make selectInputStreams throw IOE instead of RTE (todd)
+
+HDFS-3726. If a logger misses an RPC, don't retry that logger until next segment (todd)
+
+HDFS-3893. QJM: Make QJM work with security enabled. (atm)
+
+HDFS-3897. QJM: TestBlockToken fails after HDFS-3893. (atm)
+
+HDFS-3898. QJM: enable TCP_NODELAY for IPC (todd)
+
+HDFS-3885. QJM: optimize log sync when JN is lagging behind (todd)
+
+HDFS-3900. QJM: avoid validating log segments on log rolls (todd)
+
+HDFS-3901. QJM: send 'heartbeat' messages to JNs even when they are out-of-sync (todd)
+
+HDFS-3899. QJM: Add client-side metrics (todd)
+
+HDFS-3914. QJM: acceptRecovery should abort current segment (todd)
+
+HDFS-3915. QJM: Failover fails with auth error in secure cluster (todd)
+
+HDFS-3906. QJM: quorum timeout on failover with large log segment (todd)
+
+HDFS-3840. JournalNodes log JournalNotFormattedException backtrace error before being formatted (todd)
+
+HDFS-3894. QJM: testRecoverAfterDoubleFailures can be flaky due to IPC client caching (todd)
+
+HDFS-3926. QJM: Add user documentation for QJM. (atm)
+
+HDFS-3943. QJM: remove currently-unused md5sum field (todd)
+
+HDFS-3950. QJM: misc TODO cleanup, improved log messages, etc. (todd)
+
+HDFS-3955. QJM: Make acceptRecovery() atomic. (todd)
+
+HDFS-3956. QJM: purge temporary files when no longer within retention period (todd)
+
+HDFS-4004. TestJournalNode#testJournal fails because of test case execution order (Chao Shi via todd)
+
+HDFS-4017. Unclosed FileInputStream in GetJournalEditServlet (Chao Shi via todd)
diff --git a/hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml b/hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml
index 7c9f364..fdaccb9 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml
+++ b/hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml
@@ -9,6 +9,9 @@
        <Package name="org.apache.hadoop.hdfs.server.namenode.ha.proto" />
      </Match>
      <Match>
+       <Package name="org.apache.hadoop.hdfs.qjournal.protocol" />
+     </Match>
+     <Match>
        <Bug pattern="EI_EXPOSE_REP" />
      </Match>
      <Match>
@@ -273,10 +276,18 @@
        <Method name="quit" />
        <Bug pattern="DM_EXIT" />
      </Match>
+
      <!-- Don't complain about recoverBlock equality check -->
      <Match>
        <Class name="org.apache.hadoop.hdfs.server.datanode.DataNode" />
        <Method name="recoverBlock" />
        <Bug pattern="EC_UNRELATED_TYPES" />
      </Match>
+
+     <!-- More complex cleanup logic confuses findbugs -->
+     <Match>
+       <Class name="org.apache.hadoop.hdfs.qjournal.server.Journal" />
+       <Method name="persistPaxosData" />
+       <Bug pattern="OS_OPEN_STREAM" />
+     </Match>
  </FindBugsFilter>
diff --git a/hadoop-hdfs-project/hadoop-hdfs/pom.xml b/hadoop-hdfs-project/hadoop-hdfs/pom.xml
index df7405ca..c5d45b1 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/pom.xml
+++ b/hadoop-hdfs-project/hadoop-hdfs/pom.xml
@@ -240,6 +240,25 @@
             </configuration>
           </execution>
           <execution>
+            <id>journal</id>
+            <phase>generate-sources</phase>
+            <goals>
+              <goal>compile</goal>
+            </goals>
+            <configuration>
+              <compile>false</compile>
+              <workingDirectory>${project.build.directory}/generated-src/main/jsp</workingDirectory>
+              <webFragmentFile>${project.build.directory}/journal-jsp-servlet-definitions.xml</webFragmentFile>
+              <packageName>org.apache.hadoop.hdfs.server.journalservice</packageName>
+              <sources>
+                <directory>${basedir}/src/main/webapps/journal</directory>
+                <includes>
+                  <include>*.jsp</include>
+                </includes>
+              </sources>
+            </configuration>
+          </execution>
+          <execution>
             <id>datanode</id>
             <phase>generate-sources</phase>
             <goals>
@@ -349,6 +368,7 @@
                 <loadfile property="hdfs.servlet.definitions" srcFile="${project.build.directory}/hdfs-jsp-servlet-definitions.xml"/>
                 <loadfile property="secondary.servlet.definitions" srcFile="${project.build.directory}/secondary-jsp-servlet-definitions.xml"/>
                 <loadfile property="datanode.servlet.definitions" srcFile="${project.build.directory}/datanode-jsp-servlet-definitions.xml"/>
+                <loadfile property="journal.servlet.definitions" srcFile="${project.build.directory}/journal-jsp-servlet-definitions.xml"/>               
                 <echoproperties destfile="${project.build.directory}/webxml.properties">
                   <propertyset>
                     <propertyref regex=".*.servlet.definitions"/>
@@ -364,6 +384,9 @@
                 <copy file="${basedir}/src/main/webapps/proto-datanode-web.xml"
                       tofile="${project.build.directory}/webapps/datanode/WEB-INF/web.xml"
                       filtering="true"/>
+                <copy file="${basedir}/src/main/webapps/proto-journal-web.xml"
+                      tofile="${project.build.directory}/webapps/journal/WEB-INF/web.xml"
+                      filtering="true"/>
                 <copy toDir="${project.build.directory}/webapps">
                   <fileset dir="${basedir}/src/main/webapps">
                     <exclude name="**/*.jsp"/>
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/contrib/bkjournal/src/main/java/org/apache/hadoop/contrib/bkjournal/BookKeeperEditLogOutputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/contrib/bkjournal/src/main/java/org/apache/hadoop/contrib/bkjournal/BookKeeperEditLogOutputStream.java
index 6267871..4cc4b2d 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/contrib/bkjournal/src/main/java/org/apache/hadoop/contrib/bkjournal/BookKeeperEditLogOutputStream.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/contrib/bkjournal/src/main/java/org/apache/hadoop/contrib/bkjournal/BookKeeperEditLogOutputStream.java
@@ -84,7 +84,7 @@
   @Override
   public void close() throws IOException {
     setReadyToFlush();
-    flushAndSync();
+    flushAndSync(true);
     try {
       lh.close();
     } catch (InterruptedException ie) {
@@ -130,7 +130,7 @@
   }
 
   @Override
-  public void flushAndSync() throws IOException {
+  public void flushAndSync(boolean durable) throws IOException {
     assert(syncLatch != null);
     try {
       syncLatch.await();
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/bin/hdfs b/hadoop-hdfs-project/hadoop-hdfs/src/main/bin/hdfs
index 2b446d1..d7aef66 100755
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/bin/hdfs
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/bin/hdfs
@@ -30,6 +30,7 @@
   echo "  namenode -format     format the DFS filesystem"
   echo "  secondarynamenode    run the DFS secondary namenode"
   echo "  namenode             run the DFS namenode"
+  echo "  journalnode          run the DFS journalnode"
   echo "  zkfc                 run the ZK Failover Controller daemon"
   echo "  datanode             run a DFS datanode"
   echo "  dfsadmin             run a DFS admin client"
@@ -90,6 +91,9 @@
   else
     HADOOP_OPTS="$HADOOP_OPTS -server $HADOOP_DATANODE_OPTS"
   fi
+elif [ "$COMMAND" = "journalnode" ] ; then
+  CLASS='org.apache.hadoop.hdfs.qjournal.server.JournalNode'
+  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_JOURNALNODE_OPTS"
 elif [ "$COMMAND" = "dfs" ] ; then
   CLASS=org.apache.hadoop.fs.FsShell
   HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
index 441a905..918a790 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
@@ -395,4 +395,42 @@
   public static final String DFS_ENCRYPT_DATA_TRANSFER_KEY = "dfs.encrypt.data.transfer";
   public static final boolean DFS_ENCRYPT_DATA_TRANSFER_DEFAULT = false;
   public static final String DFS_DATA_ENCRYPTION_ALGORITHM_KEY = "dfs.encrypt.data.transfer.algorithm";
+  
+  // Journal-node related configs. These are read on the JN side.
+  public static final String  DFS_JOURNALNODE_EDITS_DIR_KEY = "dfs.journalnode.edits.dir";
+  public static final String  DFS_JOURNALNODE_EDITS_DIR_DEFAULT = "/tmp/hadoop/dfs/journalnode/";
+  public static final String  DFS_JOURNALNODE_RPC_ADDRESS_KEY = "dfs.journalnode.rpc-address";
+  public static final int     DFS_JOURNALNODE_RPC_PORT_DEFAULT = 8485;
+  public static final String  DFS_JOURNALNODE_RPC_ADDRESS_DEFAULT = "0.0.0.0:" + DFS_JOURNALNODE_RPC_PORT_DEFAULT;
+    
+  public static final String  DFS_JOURNALNODE_HTTP_ADDRESS_KEY = "dfs.journalnode.http-address";
+  public static final int     DFS_JOURNALNODE_HTTP_PORT_DEFAULT = 8480;
+  public static final String  DFS_JOURNALNODE_HTTP_ADDRESS_DEFAULT = "0.0.0.0:" + DFS_JOURNALNODE_HTTP_PORT_DEFAULT;
+
+  public static final String  DFS_JOURNALNODE_KEYTAB_FILE_KEY = "dfs.journalnode.keytab.file";
+  public static final String  DFS_JOURNALNODE_USER_NAME_KEY = "dfs.journalnode.kerberos.principal";
+  public static final String  DFS_JOURNALNODE_INTERNAL_SPNEGO_USER_NAME_KEY = "dfs.journalnode.kerberos.internal.spnego.principal";
+
+  // Journal-node related configs for the client side.
+  public static final String  DFS_QJOURNAL_QUEUE_SIZE_LIMIT_KEY = "dfs.qjournal.queued-edits.limit.mb";
+  public static final int     DFS_QJOURNAL_QUEUE_SIZE_LIMIT_DEFAULT = 10;
+  
+  // Quorum-journal timeouts for various operations. Unlikely to need
+  // to be tweaked, but configurable just in case.
+  public static final String  DFS_QJOURNAL_START_SEGMENT_TIMEOUT_KEY = "dfs.qjournal.start-segment.timeout.ms";
+  public static final String  DFS_QJOURNAL_PREPARE_RECOVERY_TIMEOUT_KEY = "dfs.qjournal.prepare-recovery.timeout.ms";
+  public static final String  DFS_QJOURNAL_ACCEPT_RECOVERY_TIMEOUT_KEY = "dfs.qjournal.accept-recovery.timeout.ms";
+  public static final String  DFS_QJOURNAL_FINALIZE_SEGMENT_TIMEOUT_KEY = "dfs.qjournal.finalize-segment.timeout.ms";
+  public static final String  DFS_QJOURNAL_SELECT_INPUT_STREAMS_TIMEOUT_KEY = "dfs.qjournal.select-input-streams.timeout.ms";
+  public static final String  DFS_QJOURNAL_GET_JOURNAL_STATE_TIMEOUT_KEY = "dfs.qjournal.get-journal-state.timeout.ms";
+  public static final String  DFS_QJOURNAL_NEW_EPOCH_TIMEOUT_KEY = "dfs.qjournal.new-epoch.timeout.ms";
+  public static final String  DFS_QJOURNAL_WRITE_TXNS_TIMEOUT_KEY = "dfs.qjournal.write-txns.timeout.ms";
+  public static final int     DFS_QJOURNAL_START_SEGMENT_TIMEOUT_DEFAULT = 20000;
+  public static final int     DFS_QJOURNAL_PREPARE_RECOVERY_TIMEOUT_DEFAULT = 120000;
+  public static final int     DFS_QJOURNAL_ACCEPT_RECOVERY_TIMEOUT_DEFAULT = 120000;
+  public static final int     DFS_QJOURNAL_FINALIZE_SEGMENT_TIMEOUT_DEFAULT = 120000;
+  public static final int     DFS_QJOURNAL_SELECT_INPUT_STREAMS_TIMEOUT_DEFAULT = 20000;
+  public static final int     DFS_QJOURNAL_GET_JOURNAL_STATE_TIMEOUT_DEFAULT = 120000;
+  public static final int     DFS_QJOURNAL_NEW_EPOCH_TIMEOUT_DEFAULT = 120000;
+  public static final int     DFS_QJOURNAL_WRITE_TXNS_TIMEOUT_DEFAULT = 20000;
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSUtil.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSUtil.java
index a64a29d..27130c3 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSUtil.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSUtil.java
@@ -75,6 +75,7 @@
 import org.apache.hadoop.ipc.RPC;
 import org.apache.hadoop.net.NetUtils;
 import org.apache.hadoop.net.NodeBase;
+import org.apache.hadoop.security.SecurityUtil;
 import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.util.StringUtils;
 import org.apache.hadoop.util.ToolRunner;
@@ -488,6 +489,34 @@
   }
 
   /**
+   * @return a collection of all configured NN Kerberos principals.
+   */
+  public static Set<String> getAllNnPrincipals(Configuration conf) throws IOException {
+    Set<String> principals = new HashSet<String>();
+    for (String nsId : DFSUtil.getNameServiceIds(conf)) {
+      if (HAUtil.isHAEnabled(conf, nsId)) {
+        for (String nnId : DFSUtil.getNameNodeIds(conf, nsId)) {
+          Configuration confForNn = new Configuration(conf);
+          NameNode.initializeGenericKeys(confForNn, nsId, nnId);
+          String principal = SecurityUtil.getServerPrincipal(confForNn
+              .get(DFSConfigKeys.DFS_NAMENODE_USER_NAME_KEY),
+              NameNode.getAddress(confForNn).getHostName());
+          principals.add(principal);
+        }
+      } else {
+        Configuration confForNn = new Configuration(conf);
+        NameNode.initializeGenericKeys(confForNn, nsId, null);
+        String principal = SecurityUtil.getServerPrincipal(confForNn
+            .get(DFSConfigKeys.DFS_NAMENODE_USER_NAME_KEY),
+            NameNode.getAddress(confForNn).getHostName());
+        principals.add(principal);
+      }
+    }
+
+    return principals;
+  }
+
+  /**
    * Returns list of InetSocketAddress corresponding to HA NN RPC addresses from
    * the configuration.
    * 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/HDFSPolicyProvider.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/HDFSPolicyProvider.java
index e8e80a8..7268edd 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/HDFSPolicyProvider.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/HDFSPolicyProvider.java
@@ -23,6 +23,7 @@
 import org.apache.hadoop.ha.ZKFCProtocol;
 import org.apache.hadoop.hdfs.protocol.ClientDatanodeProtocol;
 import org.apache.hadoop.hdfs.protocol.ClientProtocol;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
 import org.apache.hadoop.hdfs.server.protocol.DatanodeProtocol;
 import org.apache.hadoop.hdfs.server.protocol.InterDatanodeProtocol;
 import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocol;
@@ -46,6 +47,7 @@
     new Service("security.inter.datanode.protocol.acl", 
                 InterDatanodeProtocol.class),
     new Service("security.namenode.protocol.acl", NamenodeProtocol.class),
+    new Service("security.qjournal.service.protocol.acl", QJournalProtocol.class),
     new Service(CommonConfigurationKeys.SECURITY_HA_SERVICE_PROTOCOL_ACL,
         HAServiceProtocol.class),
     new Service(CommonConfigurationKeys.SECURITY_ZKFC_PROTOCOL_ACL,
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/PBHelper.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/PBHelper.java
index 09032ba..2d33558 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/PBHelper.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/PBHelper.java
@@ -326,12 +326,15 @@
   }
 
   public static RemoteEditLogProto convert(RemoteEditLog log) {
-    return RemoteEditLogProto.newBuilder().setEndTxId(log.getEndTxId())
-        .setStartTxId(log.getStartTxId()).build();
+    return RemoteEditLogProto.newBuilder()
+        .setStartTxId(log.getStartTxId())
+        .setEndTxId(log.getEndTxId())
+        .setIsInProgress(log.isInProgress()).build();
   }
 
   public static RemoteEditLog convert(RemoteEditLogProto l) {
-    return new RemoteEditLog(l.getStartTxId(), l.getEndTxId());
+    return new RemoteEditLog(l.getStartTxId(), l.getEndTxId(),
+        l.getIsInProgress());
   }
 
   public static RemoteEditLogManifestProto convert(
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/AsyncLogger.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/AsyncLogger.java
new file mode 100644
index 0000000..99b9d6b
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/AsyncLogger.java
@@ -0,0 +1,154 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.net.InetSocketAddress;
+import java.net.URL;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.server.protocol.RemoteEditLogManifest;
+
+import com.google.common.util.concurrent.ListenableFuture;
+
+/**
+ * Interface for a remote log which is only communicated with asynchronously.
+ * This is essentially a wrapper around {@link QJournalProtocol} with the key
+ * differences being:
+ * 
+ * <ul>
+ * <li>All methods return {@link ListenableFuture}s instead of synchronous
+ * objects.</li>
+ * <li>The {@link RequestInfo} objects are created by the underlying
+ * implementation.</li>
+ * </ul>
+ */
+interface AsyncLogger {
+  
+  interface Factory {
+    AsyncLogger createLogger(Configuration conf, NamespaceInfo nsInfo,
+        String journalId, InetSocketAddress addr);
+  }
+
+  /**
+   * Send a batch of edits to the logger.
+   * @param segmentTxId the first txid in the current segment
+   * @param firstTxnId the first txid of the edits.
+   * @param numTxns the number of transactions in the batch
+   * @param data the actual data to be sent
+   */
+  public ListenableFuture<Void> sendEdits(
+      final long segmentTxId, final long firstTxnId,
+      final int numTxns, final byte[] data);
+
+  /**
+   * Begin writing a new log segment.
+   * 
+   * @param txid the first txid to be written to the new log
+   */
+  public ListenableFuture<Void> startLogSegment(long txid);
+
+  /**
+   * Finalize a log segment.
+   * 
+   * @param startTxId the first txid that was written to the segment
+   * @param endTxId the last txid that was written to the segment
+   */
+  public ListenableFuture<Void> finalizeLogSegment(
+      long startTxId, long endTxId);
+
+  /**
+   * Allow the remote node to purge edit logs earlier than this.
+   * @param minTxIdToKeep the min txid which must be retained
+   */
+  public ListenableFuture<Void> purgeLogsOlderThan(long minTxIdToKeep);
+
+  /**
+   * Format the log directory.
+   * @param nsInfo the namespace info to format with
+   */
+  public ListenableFuture<Void> format(NamespaceInfo nsInfo);
+
+  /**
+   * @return whether or not the remote node has any valid data.
+   */
+  public ListenableFuture<Boolean> isFormatted();
+  
+  /**
+   * @return the state of the last epoch on the target node.
+   */
+  public ListenableFuture<GetJournalStateResponseProto> getJournalState();
+
+  /**
+   * Begin a new epoch on the target node.
+   */
+  public ListenableFuture<NewEpochResponseProto> newEpoch(long epoch);
+  
+  /**
+   * Fetch the list of edit logs available on the remote node.
+   */
+  public ListenableFuture<RemoteEditLogManifest> getEditLogManifest(
+      long fromTxnId);
+
+  /**
+   * Prepare recovery. See the HDFS-3077 design document for details.
+   */
+  public ListenableFuture<PrepareRecoveryResponseProto> prepareRecovery(
+      long segmentTxId);
+
+  /**
+   * Accept a recovery proposal. See the HDFS-3077 design document for details.
+   */
+  public ListenableFuture<Void> acceptRecovery(SegmentStateProto log,
+      URL fromUrl);
+
+  /**
+   * Set the epoch number used for all future calls.
+   */
+  public void setEpoch(long e);
+
+  /**
+   * Let the logger know the highest committed txid across all loggers in the
+   * set. This txid may be higher than the last committed txid for <em>this</em>
+   * logger. See HDFS-3863 for details.
+   */
+  public void setCommittedTxId(long txid);
+
+  /**
+   * Build an HTTP URL to fetch the log segment with the given startTxId.
+   */
+  public URL buildURLToFetchLogs(long segmentTxId);
+  
+  /**
+   * Tear down any resources, connections, etc. The proxy may not be used
+   * after this point, and any in-flight RPCs may throw an exception.
+   */
+  public void close();
+
+  /**
+   * Append an HTML-formatted report for this logger's status to the provided
+   * StringBuilder. This is displayed on the NN web UI.
+   */
+  public void appendHtmlReport(StringBuilder sb);
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/AsyncLoggerSet.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/AsyncLoggerSet.java
new file mode 100644
index 0000000..16cd548
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/AsyncLoggerSet.java
@@ -0,0 +1,313 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.io.IOException;
+import java.net.URL;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.TimeoutException;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.server.protocol.RemoteEditLogManifest;
+import org.apache.jasper.compiler.JspUtil;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Joiner;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Maps;
+import com.google.common.util.concurrent.ListenableFuture;
+
+/**
+ * Wrapper around a set of Loggers, taking care of fanning out
+ * calls to the underlying loggers and constructing corresponding
+ * {@link QuorumCall} instances.
+ */
+class AsyncLoggerSet {
+  static final Log LOG = LogFactory.getLog(AsyncLoggerSet.class);
+
+  private final List<AsyncLogger> loggers;
+  
+  private static final long INVALID_EPOCH = -1;
+  private long myEpoch = INVALID_EPOCH;
+  
+  public AsyncLoggerSet(List<AsyncLogger> loggers) {
+    this.loggers = ImmutableList.copyOf(loggers);
+  }
+  
+  void setEpoch(long e) {
+    Preconditions.checkState(!isEpochEstablished(),
+        "Epoch already established: epoch=%s", myEpoch);
+    myEpoch = e;
+    for (AsyncLogger l : loggers) {
+      l.setEpoch(e);
+    }
+  }
+
+  /**
+   * Set the highest successfully committed txid seen by the writer.
+   * This should be called after a successful write to a quorum, and is used
+   * for extra sanity checks against the protocol. See HDFS-3863.
+   */
+  public void setCommittedTxId(long txid) {
+    for (AsyncLogger logger : loggers) {
+      logger.setCommittedTxId(txid);
+    }
+  }
+
+  /**
+   * @return true if an epoch has been established.
+   */
+  boolean isEpochEstablished() {
+    return myEpoch != INVALID_EPOCH;
+  }
+  
+  /**
+   * @return the epoch number for this writer. This may only be called after
+   * a successful call to {@link #createNewUniqueEpoch(NamespaceInfo)}.
+   */
+  long getEpoch() {
+    Preconditions.checkState(myEpoch != INVALID_EPOCH,
+        "No epoch created yet");
+    return myEpoch;
+  }
+
+  /**
+   * Close all of the underlying loggers.
+   */
+  void close() {
+    for (AsyncLogger logger : loggers) {
+      logger.close();
+    }
+  }
+  
+  void purgeLogsOlderThan(long minTxIdToKeep) {
+    for (AsyncLogger logger : loggers) {
+      logger.purgeLogsOlderThan(minTxIdToKeep);
+    }
+  }
+
+
+  /**
+   * Wait for a quorum of loggers to respond to the given call. If a quorum
+   * can't be achieved, throws a QuorumException.
+   * @param q the quorum call
+   * @param timeoutMs the number of millis to wait
+   * @param operationName textual description of the operation, for logging
+   * @return a map of successful results
+   * @throws QuorumException if a quorum doesn't respond with success
+   * @throws IOException if the thread is interrupted or times out
+   */
+  <V> Map<AsyncLogger, V> waitForWriteQuorum(QuorumCall<AsyncLogger, V> q,
+      int timeoutMs, String operationName) throws IOException {
+    int majority = getMajoritySize();
+    try {
+      q.waitFor(
+          loggers.size(), // either all respond 
+          majority, // or we get a majority successes
+          majority, // or we get a majority failures,
+          timeoutMs, operationName);
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+      throw new IOException("Interrupted waiting " + timeoutMs + "ms for a " +
+          "quorum of nodes to respond.");
+    } catch (TimeoutException e) {
+      throw new IOException("Timed out waiting " + timeoutMs + "ms for a " +
+          "quorum of nodes to respond.");
+    }
+    
+    if (q.countSuccesses() < majority) {
+      q.rethrowException("Got too many exceptions to achieve quorum size " +
+          getMajorityString());
+    }
+    
+    return q.getResults();
+  }
+  
+  /**
+   * @return the number of nodes which are required to obtain a quorum.
+   */
+  int getMajoritySize() {
+    return loggers.size() / 2 + 1;
+  }
+  
+  /**
+   * @return a textual description of the majority size (eg "2/3" or "3/5")
+   */
+  String getMajorityString() {
+    return getMajoritySize() + "/" + loggers.size();
+  }
+
+  /**
+   * @return the number of loggers behind this set
+   */
+  int size() {
+    return loggers.size();
+  }
+  
+  @Override
+  public String toString() {
+    return "[" + Joiner.on(", ").join(loggers) + "]";
+  }
+
+  /**
+   * Append an HTML-formatted status readout on the current
+   * state of the underlying loggers.
+   * @param sb the StringBuilder to append to
+   */
+  void appendHtmlReport(StringBuilder sb) {
+    sb.append("<table class=\"storage\">");
+    sb.append("<thead><tr><td>JN</td><td>Status</td></tr></thead>\n");
+    for (AsyncLogger l : loggers) {
+      sb.append("<tr>");
+      sb.append("<td>" + JspUtil.escapeXml(l.toString()) + "</td>");
+      sb.append("<td>");
+      l.appendHtmlReport(sb);
+      sb.append("</td></tr>\n");
+    }
+    sb.append("</table>");
+  }
+
+  /**
+   * @return the (mutable) list of loggers, for use in tests to
+   * set up spies
+   */
+  @VisibleForTesting
+  List<AsyncLogger> getLoggersForTests() {
+    return loggers;
+  }
+  
+  ///////////////////////////////////////////////////////////////////////////
+  // The rest of this file is simply boilerplate wrappers which fan-out the
+  // various IPC calls to the underlying AsyncLoggers and wrap the result
+  // in a QuorumCall.
+  ///////////////////////////////////////////////////////////////////////////
+  
+  public QuorumCall<AsyncLogger, GetJournalStateResponseProto> getJournalState() {
+    Map<AsyncLogger, ListenableFuture<GetJournalStateResponseProto>> calls =
+        Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      calls.put(logger, logger.getJournalState());
+    }
+    return QuorumCall.create(calls);    
+  }
+  
+  public QuorumCall<AsyncLogger, Boolean> isFormatted() {
+    Map<AsyncLogger, ListenableFuture<Boolean>> calls = Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      calls.put(logger, logger.isFormatted());
+    }
+    return QuorumCall.create(calls);
+  }
+
+  public QuorumCall<AsyncLogger,NewEpochResponseProto> newEpoch(
+      NamespaceInfo nsInfo,
+      long epoch) {
+    Map<AsyncLogger, ListenableFuture<NewEpochResponseProto>> calls =
+        Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      calls.put(logger, logger.newEpoch(epoch));
+    }
+    return QuorumCall.create(calls);    
+  }
+
+  public QuorumCall<AsyncLogger, Void> startLogSegment(
+      long txid) {
+    Map<AsyncLogger, ListenableFuture<Void>> calls = Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      calls.put(logger, logger.startLogSegment(txid));
+    }
+    return QuorumCall.create(calls);
+  }
+  
+  public QuorumCall<AsyncLogger, Void> finalizeLogSegment(long firstTxId,
+      long lastTxId) {
+    Map<AsyncLogger, ListenableFuture<Void>> calls = Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      calls.put(logger, logger.finalizeLogSegment(firstTxId, lastTxId));
+    }
+    return QuorumCall.create(calls);
+  }
+  
+  public QuorumCall<AsyncLogger, Void> sendEdits(
+      long segmentTxId, long firstTxnId, int numTxns, byte[] data) {
+    Map<AsyncLogger, ListenableFuture<Void>> calls = Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      ListenableFuture<Void> future = 
+        logger.sendEdits(segmentTxId, firstTxnId, numTxns, data);
+      calls.put(logger, future);
+    }
+    return QuorumCall.create(calls);
+  }
+
+  public QuorumCall<AsyncLogger, RemoteEditLogManifest>
+      getEditLogManifest(long fromTxnId) {
+    Map<AsyncLogger,
+        ListenableFuture<RemoteEditLogManifest>> calls
+        = Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      ListenableFuture<RemoteEditLogManifest> future =
+          logger.getEditLogManifest(fromTxnId);
+      calls.put(logger, future);
+    }
+    return QuorumCall.create(calls);
+  }
+
+  QuorumCall<AsyncLogger, PrepareRecoveryResponseProto>
+      prepareRecovery(long segmentTxId) {
+    Map<AsyncLogger,
+      ListenableFuture<PrepareRecoveryResponseProto>> calls
+      = Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      ListenableFuture<PrepareRecoveryResponseProto> future =
+          logger.prepareRecovery(segmentTxId);
+      calls.put(logger, future);
+    }
+    return QuorumCall.create(calls);
+  }
+
+  QuorumCall<AsyncLogger,Void>
+      acceptRecovery(SegmentStateProto log, URL fromURL) {
+    Map<AsyncLogger, ListenableFuture<Void>> calls
+      = Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      ListenableFuture<Void> future =
+          logger.acceptRecovery(log, fromURL);
+      calls.put(logger, future);
+    }
+    return QuorumCall.create(calls);
+  }
+
+  QuorumCall<AsyncLogger,Void> format(NamespaceInfo nsInfo) {
+    Map<AsyncLogger, ListenableFuture<Void>> calls =
+        Maps.newHashMap();
+    for (AsyncLogger logger : loggers) {
+      ListenableFuture<Void> future =
+          logger.format(nsInfo);
+      calls.put(logger, future);
+    }
+    return QuorumCall.create(calls);
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannel.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannel.java
new file mode 100644
index 0000000..1c82af8
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannel.java
@@ -0,0 +1,588 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.security.PrivilegedExceptionAction;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.protocol.HdfsConstants;
+import org.apache.hadoop.hdfs.protocolPB.PBHelper;
+import org.apache.hadoop.hdfs.qjournal.protocol.JournalOutOfSyncException;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetEditLogManifestResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
+import org.apache.hadoop.hdfs.qjournal.protocolPB.QJournalProtocolPB;
+import org.apache.hadoop.hdfs.qjournal.protocolPB.QJournalProtocolTranslatorPB;
+import org.apache.hadoop.hdfs.qjournal.server.GetJournalEditServlet;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.server.protocol.RemoteEditLogManifest;
+import org.apache.hadoop.ipc.ProtobufRpcEngine;
+import org.apache.hadoop.ipc.RPC;
+import org.apache.hadoop.security.SecurityUtil;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import com.google.common.base.Stopwatch;
+import com.google.common.net.InetAddresses;
+import com.google.common.util.concurrent.FutureCallback;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.ListeningExecutorService;
+import com.google.common.util.concurrent.MoreExecutors;
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
+import com.google.common.util.concurrent.UncaughtExceptionHandlers;
+
+/**
+ * Channel to a remote JournalNode using Hadoop IPC.
+ * All of the calls are run on a separate thread, and return
+ * {@link ListenableFuture} instances to wait for their result.
+ * This allows calls to be bound together using the {@link QuorumCall}
+ * class.
+ */
+@InterfaceAudience.Private
+public class IPCLoggerChannel implements AsyncLogger {
+
+  private final Configuration conf;
+  protected final InetSocketAddress addr;
+  private QJournalProtocol proxy;
+
+  private final ListeningExecutorService executor;
+  private long ipcSerial = 0;
+  private long epoch = -1;
+  private long committedTxId = HdfsConstants.INVALID_TXID;
+  
+  private final String journalId;
+  private final NamespaceInfo nsInfo;
+  private int httpPort = -1;
+  
+  private final IPCLoggerChannelMetrics metrics;
+  
+  /**
+   * The number of bytes of edits data still in the queue.
+   */
+  private int queuedEditsSizeBytes = 0;
+  
+  /**
+   * The highest txid that has been successfully logged on the remote JN.
+   */
+  private long highestAckedTxId = 0;
+
+  /**
+   * Nanotime of the last time we successfully journaled some edits
+   * to the remote node.
+   */
+  private long lastAckNanos = 0;
+
+  /**
+   * Nanotime of the last time that committedTxId was update. Used
+   * to calculate the lag in terms of time, rather than just a number
+   * of txns.
+   */
+  private long lastCommitNanos = 0;
+  
+  /**
+   * The maximum number of bytes that can be pending in the queue.
+   * This keeps the writer from hitting OOME if one of the loggers
+   * starts responding really slowly. Eventually, the queue
+   * overflows and it starts to treat the logger as having errored.
+   */
+  private final int queueSizeLimitBytes;
+
+  /**
+   * If this logger misses some edits, or restarts in the middle of
+   * a segment, the writer won't be able to write any more edits until
+   * the beginning of the next segment. Upon detecting this situation,
+   * the writer sets this flag to true to avoid sending useless RPCs.
+   */
+  private boolean outOfSync = false;
+  
+  /**
+   * Stopwatch which starts counting on each heartbeat that is sent
+   */
+  private Stopwatch lastHeartbeatStopwatch = new Stopwatch();
+  
+  private static final long HEARTBEAT_INTERVAL_MILLIS = 1000;
+  
+  static final Factory FACTORY = new AsyncLogger.Factory() {
+    @Override
+    public AsyncLogger createLogger(Configuration conf, NamespaceInfo nsInfo,
+        String journalId, InetSocketAddress addr) {
+      return new IPCLoggerChannel(conf, nsInfo, journalId, addr);
+    }
+  };
+
+  public IPCLoggerChannel(Configuration conf,
+      NamespaceInfo nsInfo,
+      String journalId,
+      InetSocketAddress addr) {
+    this.conf = conf;
+    this.nsInfo = nsInfo;
+    this.journalId = journalId;
+    this.addr = addr;
+    
+    this.queueSizeLimitBytes = 1024 * 1024 * conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_QUEUE_SIZE_LIMIT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_QUEUE_SIZE_LIMIT_DEFAULT);
+    
+    executor = MoreExecutors.listeningDecorator(
+        createExecutor());
+    
+    metrics = IPCLoggerChannelMetrics.create(this);
+  }
+  
+  @Override
+  public synchronized void setEpoch(long epoch) {
+    this.epoch = epoch;
+  }
+  
+  @Override
+  public synchronized void setCommittedTxId(long txid) {
+    Preconditions.checkArgument(txid >= committedTxId,
+        "Trying to move committed txid backwards in client " +
+         "old: %s new: %s", committedTxId, txid);
+    this.committedTxId = txid;
+    this.lastCommitNanos = System.nanoTime();
+  }
+  
+  @Override
+  public void close() {
+    // No more tasks may be submitted after this point.
+    executor.shutdown();
+    if (proxy != null) {
+      // TODO: this can hang for quite some time if the client
+      // is currently in the middle of a call to a downed JN.
+      // We should instead do this asynchronously, and just stop
+      // making any more calls after this point (eg clear the queue)
+      RPC.stopProxy(proxy);
+    }
+  }
+  
+  protected QJournalProtocol getProxy() throws IOException {
+    if (proxy != null) return proxy;
+    proxy = createProxy();
+    return proxy;
+  }
+  
+  protected QJournalProtocol createProxy() throws IOException {
+    final Configuration confCopy = new Configuration(conf);
+    
+    // Need to set NODELAY or else batches larger than MTU can trigger 
+    // 40ms nagling delays.
+    confCopy.setBoolean(
+        CommonConfigurationKeysPublic.IPC_CLIENT_TCPNODELAY_KEY,
+        true);
+    
+    RPC.setProtocolEngine(confCopy,
+        QJournalProtocolPB.class, ProtobufRpcEngine.class);
+    return SecurityUtil.doAsLoginUser(
+        new PrivilegedExceptionAction<QJournalProtocol>() {
+          @Override
+          public QJournalProtocol run() throws IOException {
+            RPC.setProtocolEngine(confCopy,
+                QJournalProtocolPB.class, ProtobufRpcEngine.class);
+            QJournalProtocolPB pbproxy = RPC.getProxy(
+                QJournalProtocolPB.class,
+                RPC.getProtocolVersion(QJournalProtocolPB.class),
+                addr, confCopy);
+            return new QJournalProtocolTranslatorPB(pbproxy);
+          }
+        });
+  }
+  
+  
+  /**
+   * Separated out for easy overriding in tests.
+   */
+  @VisibleForTesting
+  protected ExecutorService createExecutor() {
+    return Executors.newSingleThreadExecutor(
+        new ThreadFactoryBuilder()
+          .setDaemon(true)
+          .setNameFormat("Logger channel to " + addr)
+          .setUncaughtExceptionHandler(
+              UncaughtExceptionHandlers.systemExit())
+          .build());
+  }
+  
+  @Override
+  public URL buildURLToFetchLogs(long segmentTxId) {
+    Preconditions.checkArgument(segmentTxId > 0,
+        "Invalid segment: %s", segmentTxId);
+    Preconditions.checkState(httpPort != -1,
+        "HTTP port not set yet");
+        
+    try {
+      String path = GetJournalEditServlet.buildPath(
+          journalId, segmentTxId, nsInfo);
+      return new URL("http", addr.getHostName(), httpPort, path.toString());
+    } catch (MalformedURLException e) {
+      // should never get here.
+      throw new RuntimeException(e);
+    }
+  }
+
+  private synchronized RequestInfo createReqInfo() {
+    Preconditions.checkState(epoch > 0, "bad epoch: " + epoch);
+    return new RequestInfo(journalId, epoch, ipcSerial++,
+        committedTxId);
+  }
+
+  @VisibleForTesting
+  synchronized long getNextIpcSerial() {
+    return ipcSerial;
+  }
+
+  public synchronized int getQueuedEditsSize() {
+    return queuedEditsSizeBytes;
+  }
+  
+  public InetSocketAddress getRemoteAddress() {
+    return addr;
+  }
+
+  /**
+   * @return true if the server has gotten out of sync from the client,
+   * and thus a log roll is required for this logger to successfully start
+   * logging more edits.
+   */
+  public synchronized boolean isOutOfSync() {
+    return outOfSync;
+  }
+  
+  @VisibleForTesting
+  void waitForAllPendingCalls() throws InterruptedException {
+    try {
+      executor.submit(new Runnable() {
+        @Override
+        public void run() {
+        }
+      }).get();
+    } catch (ExecutionException e) {
+      // This can't happen!
+      throw new AssertionError(e);
+    }
+  }
+
+  @Override
+  public ListenableFuture<Boolean> isFormatted() {
+    return executor.submit(new Callable<Boolean>() {
+      @Override
+      public Boolean call() throws IOException {
+        return getProxy().isFormatted(journalId);
+      }
+    });
+  }
+
+  @Override
+  public ListenableFuture<GetJournalStateResponseProto> getJournalState() {
+    return executor.submit(new Callable<GetJournalStateResponseProto>() {
+      @Override
+      public GetJournalStateResponseProto call() throws IOException {
+        GetJournalStateResponseProto ret =
+            getProxy().getJournalState(journalId);
+        httpPort = ret.getHttpPort();
+        return ret;
+      }
+    });
+  }
+
+  @Override
+  public ListenableFuture<NewEpochResponseProto> newEpoch(
+      final long epoch) {
+    return executor.submit(new Callable<NewEpochResponseProto>() {
+      @Override
+      public NewEpochResponseProto call() throws IOException {
+        return getProxy().newEpoch(journalId, nsInfo, epoch);
+      }
+    });
+  }
+  
+  @Override
+  public ListenableFuture<Void> sendEdits(
+      final long segmentTxId, final long firstTxnId,
+      final int numTxns, final byte[] data) {
+    try {
+      reserveQueueSpace(data.length);
+    } catch (LoggerTooFarBehindException e) {
+      return Futures.immediateFailedFuture(e);
+    }
+    
+    // When this batch is acked, we use its submission time in order
+    // to calculate how far we are lagging.
+    final long submitNanos = System.nanoTime();
+    
+    ListenableFuture<Void> ret = null;
+    try {
+      ret = executor.submit(new Callable<Void>() {
+        @Override
+        public Void call() throws IOException {
+          throwIfOutOfSync();
+
+          long rpcSendTimeNanos = System.nanoTime();
+          try {
+            getProxy().journal(createReqInfo(),
+                segmentTxId, firstTxnId, numTxns, data);
+          } catch (IOException e) {
+            QuorumJournalManager.LOG.warn(
+                "Remote journal " + IPCLoggerChannel.this + " failed to " +
+                "write txns " + firstTxnId + "-" + (firstTxnId + numTxns - 1) +
+                ". Will try to write to this JN again after the next " +
+                "log roll.", e); 
+            synchronized (IPCLoggerChannel.this) {
+              outOfSync = true;
+            }
+            throw e;
+          } finally {
+            long now = System.nanoTime();
+            long rpcTime = TimeUnit.MICROSECONDS.convert(
+                now - rpcSendTimeNanos, TimeUnit.NANOSECONDS);
+            long endToEndTime = TimeUnit.MICROSECONDS.convert(
+                now - submitNanos, TimeUnit.NANOSECONDS);
+            metrics.addWriteEndToEndLatency(endToEndTime);
+            metrics.addWriteRpcLatency(rpcTime);
+          }
+          synchronized (IPCLoggerChannel.this) {
+            highestAckedTxId = firstTxnId + numTxns - 1;
+            lastAckNanos = submitNanos;
+          }
+          return null;
+        }
+      });
+    } finally {
+      if (ret == null) {
+        // it didn't successfully get submitted,
+        // so adjust the queue size back down.
+        unreserveQueueSpace(data.length);
+      } else {
+        // It was submitted to the queue, so adjust the length
+        // once the call completes, regardless of whether it
+        // succeeds or fails.
+        Futures.addCallback(ret, new FutureCallback<Void>() {
+          @Override
+          public void onFailure(Throwable t) {
+            unreserveQueueSpace(data.length);
+          }
+
+          @Override
+          public void onSuccess(Void t) {
+            unreserveQueueSpace(data.length);
+          }
+        });
+      }
+    }
+    return ret;
+  }
+
+  private void throwIfOutOfSync()
+      throws JournalOutOfSyncException, IOException {
+    if (isOutOfSync()) {
+      // Even if we're out of sync, it's useful to send an RPC
+      // to the remote node in order to update its lag metrics, etc.
+      heartbeatIfNecessary();
+      throw new JournalOutOfSyncException(
+          "Journal disabled until next roll");
+    }
+  }
+
+  /**
+   * When we've entered an out-of-sync state, it's still useful to periodically
+   * send an empty RPC to the server, such that it has the up to date
+   * committedTxId. This acts as a sanity check during recovery, and also allows
+   * that node's metrics to be up-to-date about its lag.
+   * 
+   * In the future, this method may also be used in order to check that the
+   * current node is still the current writer, even if no edits are being
+   * written.
+   */
+  private void heartbeatIfNecessary() throws IOException {
+    if (lastHeartbeatStopwatch.elapsedMillis() > HEARTBEAT_INTERVAL_MILLIS ||
+        !lastHeartbeatStopwatch.isRunning()) {
+      try {
+        getProxy().heartbeat(createReqInfo());
+      } finally {
+        // Don't send heartbeats more often than the configured interval,
+        // even if they fail.
+        lastHeartbeatStopwatch.reset().start();
+      }
+    }
+  }
+
+  private synchronized void reserveQueueSpace(int size)
+      throws LoggerTooFarBehindException {
+    Preconditions.checkArgument(size >= 0);
+    if (queuedEditsSizeBytes + size > queueSizeLimitBytes &&
+        queuedEditsSizeBytes > 0) {
+      throw new LoggerTooFarBehindException();
+    }
+    queuedEditsSizeBytes += size;
+  }
+  
+  private synchronized void unreserveQueueSpace(int size) {
+    Preconditions.checkArgument(size >= 0);
+    queuedEditsSizeBytes -= size;
+  }
+
+  @Override
+  public ListenableFuture<Void> format(final NamespaceInfo nsInfo) {
+    return executor.submit(new Callable<Void>() {
+      @Override
+      public Void call() throws Exception {
+        getProxy().format(journalId, nsInfo);
+        return null;
+      }
+    });
+  }
+  
+  @Override
+  public ListenableFuture<Void> startLogSegment(final long txid) {
+    return executor.submit(new Callable<Void>() {
+      @Override
+      public Void call() throws IOException {
+        getProxy().startLogSegment(createReqInfo(), txid);
+        synchronized (IPCLoggerChannel.this) {
+          if (outOfSync) {
+            outOfSync = false;
+            QuorumJournalManager.LOG.info(
+                "Restarting previously-stopped writes to " +
+                IPCLoggerChannel.this + " in segment starting at txid " +
+                txid);
+          }
+        }
+        return null;
+      }
+    });
+  }
+  
+  @Override
+  public ListenableFuture<Void> finalizeLogSegment(
+      final long startTxId, final long endTxId) {
+    return executor.submit(new Callable<Void>() {
+      @Override
+      public Void call() throws IOException {
+        throwIfOutOfSync();
+        
+        getProxy().finalizeLogSegment(createReqInfo(), startTxId, endTxId);
+        return null;
+      }
+    });
+  }
+  
+  @Override
+  public ListenableFuture<Void> purgeLogsOlderThan(final long minTxIdToKeep) {
+    return executor.submit(new Callable<Void>() {
+      @Override
+      public Void call() throws Exception {
+        getProxy().purgeLogsOlderThan(createReqInfo(), minTxIdToKeep);
+        return null;
+      }
+    });
+  }
+
+  @Override
+  public ListenableFuture<RemoteEditLogManifest> getEditLogManifest(
+      final long fromTxnId) {
+    return executor.submit(new Callable<RemoteEditLogManifest>() {
+      @Override
+      public RemoteEditLogManifest call() throws IOException {
+        GetEditLogManifestResponseProto ret = getProxy().getEditLogManifest(
+            journalId, fromTxnId);
+        // Update the http port, since we need this to build URLs to any of the
+        // returned logs.
+        httpPort = ret.getHttpPort();
+        return PBHelper.convert(ret.getManifest());
+      }
+    });
+  }
+
+  @Override
+  public ListenableFuture<PrepareRecoveryResponseProto> prepareRecovery(
+      final long segmentTxId) {
+    return executor.submit(new Callable<PrepareRecoveryResponseProto>() {
+      @Override
+      public PrepareRecoveryResponseProto call() throws IOException {
+        if (httpPort < 0) {
+          // If the HTTP port hasn't been set yet, force an RPC call so we know
+          // what the HTTP port should be.
+          httpPort = getProxy().getJournalState(journalId).getHttpPort();
+        }
+        return getProxy().prepareRecovery(createReqInfo(), segmentTxId);
+      }
+    });
+  }
+
+  @Override
+  public ListenableFuture<Void> acceptRecovery(
+      final SegmentStateProto log, final URL url) {
+    return executor.submit(new Callable<Void>() {
+      @Override
+      public Void call() throws IOException {
+        getProxy().acceptRecovery(createReqInfo(), log, url);
+        return null;
+      }
+    });
+  }
+
+  @Override
+  public String toString() {
+    return InetAddresses.toAddrString(addr.getAddress()) + ':' +
+        addr.getPort();
+  }
+
+  @Override
+  public synchronized void appendHtmlReport(StringBuilder sb) {
+    sb.append("Written txid ").append(highestAckedTxId);
+    long behind = getLagTxns();
+    if (behind > 0) {
+      if (lastAckNanos != 0) {
+        long lagMillis = getLagTimeMillis();
+        sb.append(" (" + behind + " txns/" + lagMillis + "ms behind)");
+      } else {
+        sb.append(" (never written");
+      }
+    }
+    if (outOfSync) {
+      sb.append(" (will try to re-sync on next segment)");
+    }
+  }
+  
+  public synchronized long getLagTxns() {
+    return Math.max(committedTxId - highestAckedTxId, 0);
+  }
+  
+  public synchronized long getLagTimeMillis() {
+    return TimeUnit.MILLISECONDS.convert(
+        Math.max(lastCommitNanos - lastAckNanos, 0),
+        TimeUnit.NANOSECONDS);
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannelMetrics.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannelMetrics.java
new file mode 100644
index 0000000..fde6b99
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannelMetrics.java
@@ -0,0 +1,154 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.net.InetSocketAddress;
+import java.util.Map;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.metrics2.annotation.Metric;
+import org.apache.hadoop.metrics2.annotation.Metrics;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
+import org.apache.hadoop.metrics2.lib.MetricsRegistry;
+import org.apache.hadoop.metrics2.lib.MutableQuantiles;
+
+import com.google.common.collect.Maps;
+
+/**
+ * The metrics for a journal from the writer's perspective.
+ */
+@Metrics(about="Journal client metrics", context="dfs")
+class IPCLoggerChannelMetrics {
+  final MetricsRegistry registry = new MetricsRegistry("NameNode");
+
+  private volatile IPCLoggerChannel ch;
+  
+  private final MutableQuantiles[] writeEndToEndLatencyQuantiles;
+  private final MutableQuantiles[] writeRpcLatencyQuantiles;
+
+  
+  /**
+   * In the case of the NN transitioning between states, edit logs are closed
+   * and reopened. Thus, the IPCLoggerChannel instance that writes to a
+   * given JournalNode may change over the lifetime of the process.
+   * However, metrics2 doesn't have a function to unregister a set of metrics
+   * and fails if a new metrics class is registered with the same name
+   * as the existing one. Hence, we have to maintain our own registry
+   * ("multiton") here, so that we have exactly one metrics instance
+   * per JournalNode, and switch out the pointer to the underlying
+   * IPCLoggerChannel instance.
+   */
+  private static final Map<String, IPCLoggerChannelMetrics> REGISTRY =
+      Maps.newHashMap();
+  
+  private IPCLoggerChannelMetrics(IPCLoggerChannel ch) {
+    this.ch = ch;
+    
+    Configuration conf = new HdfsConfiguration();
+    int[] intervals = 
+        conf.getInts(DFSConfigKeys.DFS_METRICS_PERCENTILES_INTERVALS_KEY);
+    if (intervals != null) {
+      writeEndToEndLatencyQuantiles = new MutableQuantiles[intervals.length];
+      writeRpcLatencyQuantiles = new MutableQuantiles[intervals.length];
+      for (int i = 0; i < writeEndToEndLatencyQuantiles.length; i++) {
+        int interval = intervals[i];
+        writeEndToEndLatencyQuantiles[i] = registry.newQuantiles(
+            "writesE2E" + interval + "s",
+            "End-to-end time for write operations", "ops", "LatencyMicros", interval);
+        writeRpcLatencyQuantiles[i] = registry.newQuantiles(
+            "writesRpc" + interval + "s",
+            "RPC RTT for write operations", "ops", "LatencyMicros", interval);
+      }
+    } else {
+      writeEndToEndLatencyQuantiles = null;
+      writeRpcLatencyQuantiles = null;
+    }
+  }
+  
+  private void setChannel(IPCLoggerChannel ch) {
+    assert ch.getRemoteAddress().equals(this.ch.getRemoteAddress());
+    this.ch = ch;
+  }
+
+  static IPCLoggerChannelMetrics create(IPCLoggerChannel ch) {
+    String name = getName(ch);
+    synchronized (REGISTRY) {
+      IPCLoggerChannelMetrics m = REGISTRY.get(name);
+      if (m != null) {
+        m.setChannel(ch);
+      } else {
+        m = new IPCLoggerChannelMetrics(ch);
+        DefaultMetricsSystem.instance().register(name, null, m);
+        REGISTRY.put(name, m);
+      }
+      return m;
+    }
+  }
+
+  private static String getName(IPCLoggerChannel ch) {
+    InetSocketAddress addr = ch.getRemoteAddress();
+    String addrStr = addr.getAddress().getHostAddress();
+    
+    // IPv6 addresses have colons, which aren't allowed as part of
+    // MBean names. Replace with '.'
+    addrStr = addrStr.replace(':', '.');
+    
+    return "IPCLoggerChannel-" + addrStr +
+        "-" + addr.getPort();
+  }
+
+  @Metric("Is the remote logger out of sync with the quorum")
+  public String isOutOfSync() {
+    return Boolean.toString(ch.isOutOfSync()); 
+  }
+  
+  @Metric("The number of transactions the remote log is lagging behind the " +
+          "quorum")
+  public long getCurrentLagTxns() {
+    return ch.getLagTxns();
+  }
+  
+  @Metric("The number of milliseconds the remote log is lagging behind the " +
+          "quorum")
+  public long getLagTimeMillis() {
+    return ch.getLagTimeMillis();
+  }
+  
+  @Metric("The number of bytes of pending data to be sent to the remote node")
+  public int getQueuedEditsSize() {
+    return ch.getQueuedEditsSize();
+  }
+
+  public void addWriteEndToEndLatency(long micros) {
+    if (writeEndToEndLatencyQuantiles != null) {
+      for (MutableQuantiles q : writeEndToEndLatencyQuantiles) {
+        q.add(micros);
+      }
+    }
+  }
+  
+  public void addWriteRpcLatency(long micros) {
+    if (writeRpcLatencyQuantiles != null) {
+      for (MutableQuantiles q : writeRpcLatencyQuantiles) {
+        q.add(micros);
+      }
+    }
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/LoggerTooFarBehindException.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/LoggerTooFarBehindException.java
new file mode 100644
index 0000000..0dbf5bf
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/LoggerTooFarBehindException.java
@@ -0,0 +1,25 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.io.IOException;
+
+class LoggerTooFarBehindException extends IOException {
+  private static final long serialVersionUID = 1L;
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumCall.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumCall.java
new file mode 100644
index 0000000..c42f6b9
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumCall.java
@@ -0,0 +1,230 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.concurrent.TimeoutException;
+
+import org.apache.hadoop.ipc.RemoteException;
+import org.apache.hadoop.util.Time;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Maps;
+import com.google.common.util.concurrent.FutureCallback;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.protobuf.Message;
+import com.google.protobuf.TextFormat;
+
+/**
+ * Represents a set of calls for which a quorum of results is needed.
+ * @param <KEY> a key used to identify each of the outgoing calls
+ * @param <RESULT> the type of the call result
+ */
+class QuorumCall<KEY, RESULT> {
+  private final Map<KEY, RESULT> successes = Maps.newHashMap();
+  private final Map<KEY, Throwable> exceptions = Maps.newHashMap();
+
+  /**
+   * Interval, in milliseconds, at which a log message will be made
+   * while waiting for a quorum call.
+   */
+  private static final int WAIT_PROGRESS_INTERVAL_MILLIS = 1000;
+  
+  /**
+   * Start logging messages at INFO level periodically after waiting for
+   * this fraction of the configured timeout for any call.
+   */
+  private static final float WAIT_PROGRESS_INFO_THRESHOLD = 0.3f;
+  /**
+   * Start logging messages at WARN level after waiting for this
+   * fraction of the configured timeout for any call.
+   */
+  private static final float WAIT_PROGRESS_WARN_THRESHOLD = 0.7f;
+  
+  static <KEY, RESULT> QuorumCall<KEY, RESULT> create(
+      Map<KEY, ? extends ListenableFuture<RESULT>> calls) {
+    final QuorumCall<KEY, RESULT> qr = new QuorumCall<KEY, RESULT>();
+    for (final Entry<KEY, ? extends ListenableFuture<RESULT>> e : calls.entrySet()) {
+      Preconditions.checkArgument(e.getValue() != null,
+          "null future for key: " + e.getKey());
+      Futures.addCallback(e.getValue(), new FutureCallback<RESULT>() {
+        @Override
+        public void onFailure(Throwable t) {
+          qr.addException(e.getKey(), t);
+        }
+
+        @Override
+        public void onSuccess(RESULT res) {
+          qr.addResult(e.getKey(), res);
+        }
+      });
+    }
+    return qr;
+  }
+  
+  private QuorumCall() {
+    // Only instantiated from factory method above
+  }
+  
+  /**
+   * Wait for the quorum to achieve a certain number of responses.
+   * 
+   * Note that, even after this returns, more responses may arrive,
+   * causing the return value of other methods in this class to change.
+   *
+   * @param minResponses return as soon as this many responses have been
+   * received, regardless of whether they are successes or exceptions
+   * @param minSuccesses return as soon as this many successful (non-exception)
+   * responses have been received
+   * @param maxExceptions return as soon as this many exception responses
+   * have been received. Pass 0 to return immediately if any exception is
+   * received.
+   * @param millis the number of milliseconds to wait for
+   * @throws InterruptedException if the thread is interrupted while waiting
+   * @throws TimeoutException if the specified timeout elapses before
+   * achieving the desired conditions
+   */
+  public synchronized void waitFor(
+      int minResponses, int minSuccesses, int maxExceptions,
+      int millis, String operationName)
+      throws InterruptedException, TimeoutException {
+    long st = Time.monotonicNow();
+    long nextLogTime = st + (long)(millis * WAIT_PROGRESS_INFO_THRESHOLD);
+    long et = st + millis;
+    while (true) {
+      checkAssertionErrors();
+      if (minResponses > 0 && countResponses() >= minResponses) return;
+      if (minSuccesses > 0 && countSuccesses() >= minSuccesses) return;
+      if (maxExceptions >= 0 && countExceptions() > maxExceptions) return;
+      long now = Time.monotonicNow();
+      
+      if (now > nextLogTime) {
+        long waited = now - st;
+        String msg = String.format(
+            "Waited %s ms (timeout=%s ms) for a response for %s",
+            waited, millis, operationName);
+        if (waited > millis * WAIT_PROGRESS_WARN_THRESHOLD) {
+          QuorumJournalManager.LOG.warn(msg);
+        } else {
+          QuorumJournalManager.LOG.info(msg);
+        }
+        nextLogTime = now + WAIT_PROGRESS_INTERVAL_MILLIS;
+      }
+      long rem = et - now;
+      if (rem <= 0) {
+        throw new TimeoutException();
+      }
+      rem = Math.min(rem, nextLogTime - now);
+      rem = Math.max(rem, 1);
+      wait(rem);
+    }
+  }
+
+  /**
+   * Check if any of the responses came back with an AssertionError.
+   * If so, it re-throws it, even if there was a quorum of responses.
+   * This code only runs if assertions are enabled for this class,
+   * otherwise it should JIT itself away.
+   * 
+   * This is done since AssertionError indicates programmer confusion
+   * rather than some kind of expected issue, and thus in the context
+   * of test cases we'd like to actually fail the test case instead of
+   * continuing through.
+   */
+  private synchronized void checkAssertionErrors() {
+    boolean assertsEnabled = false;
+    assert assertsEnabled = true; // sets to true if enabled
+    if (assertsEnabled) {
+      for (Throwable t : exceptions.values()) {
+        if (t instanceof AssertionError) {
+          throw (AssertionError)t;
+        } else if (t instanceof RemoteException &&
+            ((RemoteException)t).getClassName().equals(
+                AssertionError.class.getName())) {
+          throw new AssertionError(t);
+        }
+      }
+    }
+  }
+
+  private synchronized void addResult(KEY k, RESULT res) {
+    successes.put(k, res);
+    notifyAll();
+  }
+  
+  private synchronized void addException(KEY k, Throwable t) {
+    exceptions.put(k, t);
+    notifyAll();
+  }
+  
+  /**
+   * @return the total number of calls for which a response has been received,
+   * regardless of whether it threw an exception or returned a successful
+   * result.
+   */
+  public synchronized int countResponses() {
+    return successes.size() + exceptions.size();
+  }
+  
+  /**
+   * @return the number of calls for which a non-exception response has been
+   * received.
+   */
+  public synchronized int countSuccesses() {
+    return successes.size();
+  }
+  
+  /**
+   * @return the number of calls for which an exception response has been
+   * received.
+   */
+  public synchronized int countExceptions() {
+    return exceptions.size();
+  }
+
+  /**
+   * @return the map of successful responses. A copy is made such that this
+   * map will not be further mutated, even if further results arrive for the
+   * quorum.
+   */
+  public synchronized Map<KEY, RESULT> getResults() {
+    return Maps.newHashMap(successes);
+  }
+
+  public synchronized void rethrowException(String msg) throws QuorumException {
+    Preconditions.checkState(!exceptions.isEmpty());
+    throw QuorumException.create(msg, successes, exceptions);
+  }
+
+  public static <K> String mapToString(
+      Map<K, ? extends Message> map) {
+    StringBuilder sb = new StringBuilder();
+    boolean first = true;
+    for (Map.Entry<K, ? extends Message> e : map.entrySet()) {
+      if (!first) {
+        sb.append("\n");
+      }
+      first = false;
+      sb.append(e.getKey()).append(": ")
+        .append(TextFormat.shortDebugString(e.getValue()));
+    }
+    return sb.toString();
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumException.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumException.java
new file mode 100644
index 0000000..446092e
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumException.java
@@ -0,0 +1,89 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.io.IOException;
+import java.util.Map;
+
+import org.apache.hadoop.util.StringUtils;
+
+import com.google.common.base.Joiner;
+import com.google.common.base.Preconditions;
+
+/**
+ * Exception thrown when too many exceptions occur while gathering
+ * responses to a quorum call. 
+ */
+class QuorumException extends IOException {
+
+  /**
+   * Create a QuorumException instance with a descriptive message detailing
+   * the underlying exceptions, as well as any successful responses which
+   * were returned.
+   * @param <K> the keys for the quorum calls
+   * @param <V> the success response type
+   * @param successes any successful responses returned
+   * @param exceptions the exceptions returned
+   */
+  public static <K, V> QuorumException create(
+      String simpleMsg,
+      Map<K, V> successes,
+      Map<K, Throwable> exceptions) {
+    Preconditions.checkArgument(!exceptions.isEmpty(),
+        "Must pass exceptions");
+    
+    StringBuilder msg = new StringBuilder();
+    msg.append(simpleMsg).append(". ");
+    if (!successes.isEmpty()) {
+      msg.append(successes.size()).append(" successful responses:\n");
+      
+      Joiner.on("\n")
+          .useForNull("null [success]")
+          .withKeyValueSeparator(": ")
+          .appendTo(msg, successes);
+      msg.append("\n");
+    }
+    
+    msg.append(exceptions.size() + " exceptions thrown:\n");
+    boolean isFirst = true;
+    
+    for (Map.Entry<K, Throwable> e : exceptions.entrySet()) {
+      if (!isFirst) {
+        msg.append("\n");
+      }
+      isFirst = false;
+      
+      msg.append(e.getKey()).append(": ");
+      
+      if (e.getValue() instanceof RuntimeException) {
+        msg.append(StringUtils.stringifyException(e.getValue()));
+      } else if (e.getValue().getLocalizedMessage() != null) {
+        msg.append(e.getValue().getLocalizedMessage());
+      } else {
+        msg.append(StringUtils.stringifyException(e.getValue()));
+      }
+    }
+    return new QuorumException(msg.toString());
+  }
+
+  private QuorumException(String msg) {
+    super(msg);
+  }
+
+  private static final long serialVersionUID = 1L;
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumJournalManager.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumJournalManager.java
new file mode 100644
index 0000000..6b3503d
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumJournalManager.java
@@ -0,0 +1,492 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.net.URL;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.PriorityQueue;
+import java.util.concurrent.TimeoutException;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.server.namenode.EditLogFileInputStream;
+import org.apache.hadoop.hdfs.server.namenode.EditLogInputStream;
+import org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream;
+import org.apache.hadoop.hdfs.server.namenode.JournalManager;
+import org.apache.hadoop.hdfs.server.namenode.JournalSet;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.server.protocol.RemoteEditLog;
+import org.apache.hadoop.hdfs.server.protocol.RemoteEditLogManifest;
+import org.apache.hadoop.net.NetUtils;
+import org.apache.hadoop.util.StringUtils;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Joiner;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Lists;
+import com.google.protobuf.TextFormat;
+
+/**
+ * A JournalManager that writes to a set of remote JournalNodes,
+ * requiring a quorum of nodes to ack each write.
+ */
+@InterfaceAudience.Private
+public class QuorumJournalManager implements JournalManager {
+  static final Log LOG = LogFactory.getLog(QuorumJournalManager.class);
+
+  // Timeouts for which the QJM will wait for each of the following actions.
+  private final int startSegmentTimeoutMs;
+  private final int prepareRecoveryTimeoutMs;
+  private final int acceptRecoveryTimeoutMs;
+  private final int finalizeSegmentTimeoutMs;
+  private final int selectInputStreamsTimeoutMs;
+  private final int getJournalStateTimeoutMs;
+  private final int newEpochTimeoutMs;
+  private final int writeTxnsTimeoutMs;
+
+  // Since these don't occur during normal operation, we can
+  // use rather lengthy timeouts, and don't need to make them
+  // configurable.
+  private static final int FORMAT_TIMEOUT_MS = 60000;
+  private static final int HASDATA_TIMEOUT_MS = 60000;
+  
+  private final Configuration conf;
+  private final URI uri;
+  private final NamespaceInfo nsInfo;
+  private boolean isActiveWriter;
+  
+  private final AsyncLoggerSet loggers;
+
+  private int outputBufferCapacity = 512 * 1024;
+  
+  public QuorumJournalManager(Configuration conf,
+      URI uri, NamespaceInfo nsInfo) throws IOException {
+    this(conf, uri, nsInfo, IPCLoggerChannel.FACTORY);
+  }
+  
+  QuorumJournalManager(Configuration conf,
+      URI uri, NamespaceInfo nsInfo,
+      AsyncLogger.Factory loggerFactory) throws IOException {
+    Preconditions.checkArgument(conf != null, "must be configured");
+
+    this.conf = conf;
+    this.uri = uri;
+    this.nsInfo = nsInfo;
+    this.loggers = new AsyncLoggerSet(createLoggers(loggerFactory));
+
+    // Configure timeouts.
+    this.startSegmentTimeoutMs = conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_START_SEGMENT_TIMEOUT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_START_SEGMENT_TIMEOUT_DEFAULT);
+    this.prepareRecoveryTimeoutMs = conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_PREPARE_RECOVERY_TIMEOUT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_PREPARE_RECOVERY_TIMEOUT_DEFAULT);
+    this.acceptRecoveryTimeoutMs = conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_ACCEPT_RECOVERY_TIMEOUT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_ACCEPT_RECOVERY_TIMEOUT_DEFAULT);
+    this.finalizeSegmentTimeoutMs = conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_FINALIZE_SEGMENT_TIMEOUT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_FINALIZE_SEGMENT_TIMEOUT_DEFAULT);
+    this.selectInputStreamsTimeoutMs = conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_SELECT_INPUT_STREAMS_TIMEOUT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_SELECT_INPUT_STREAMS_TIMEOUT_DEFAULT);
+    this.getJournalStateTimeoutMs = conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_GET_JOURNAL_STATE_TIMEOUT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_GET_JOURNAL_STATE_TIMEOUT_DEFAULT);
+    this.newEpochTimeoutMs = conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_NEW_EPOCH_TIMEOUT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_NEW_EPOCH_TIMEOUT_DEFAULT);
+    this.writeTxnsTimeoutMs = conf.getInt(
+        DFSConfigKeys.DFS_QJOURNAL_WRITE_TXNS_TIMEOUT_KEY,
+        DFSConfigKeys.DFS_QJOURNAL_WRITE_TXNS_TIMEOUT_DEFAULT);
+  }
+  
+  protected List<AsyncLogger> createLoggers(
+      AsyncLogger.Factory factory) throws IOException {
+    return createLoggers(conf, uri, nsInfo, factory);
+  }
+
+  static String parseJournalId(URI uri) {
+    String path = uri.getPath();
+    Preconditions.checkArgument(path != null && !path.isEmpty(),
+        "Bad URI '%s': must identify journal in path component",
+        uri);
+    String journalId = path.substring(1);
+    checkJournalId(journalId);
+    return journalId;
+  }
+  
+  public static void checkJournalId(String jid) {
+    Preconditions.checkArgument(jid != null &&
+        !jid.isEmpty() &&
+        !jid.contains("/") &&
+        !jid.startsWith("."),
+        "bad journal id: " + jid);
+  }
+
+  
+  /**
+   * Fence any previous writers, and obtain a unique epoch number
+   * for write-access to the journal nodes.
+   *
+   * @return the new, unique epoch number
+   */
+  Map<AsyncLogger, NewEpochResponseProto> createNewUniqueEpoch()
+      throws IOException {
+    Preconditions.checkState(!loggers.isEpochEstablished(),
+        "epoch already created");
+    
+    Map<AsyncLogger, GetJournalStateResponseProto> lastPromises =
+      loggers.waitForWriteQuorum(loggers.getJournalState(),
+          getJournalStateTimeoutMs, "getJournalState()");
+    
+    long maxPromised = Long.MIN_VALUE;
+    for (GetJournalStateResponseProto resp : lastPromises.values()) {
+      maxPromised = Math.max(maxPromised, resp.getLastPromisedEpoch());
+    }
+    assert maxPromised >= 0;
+    
+    long myEpoch = maxPromised + 1;
+    Map<AsyncLogger, NewEpochResponseProto> resps =
+        loggers.waitForWriteQuorum(loggers.newEpoch(nsInfo, myEpoch),
+            newEpochTimeoutMs, "newEpoch(" + myEpoch + ")");
+        
+    loggers.setEpoch(myEpoch);
+    return resps;
+  }
+  
+  @Override
+  public void format(NamespaceInfo nsInfo) throws IOException {
+    QuorumCall<AsyncLogger,Void> call = loggers.format(nsInfo);
+    try {
+      call.waitFor(loggers.size(), loggers.size(), 0, FORMAT_TIMEOUT_MS,
+          "format");
+    } catch (InterruptedException e) {
+      throw new IOException("Interrupted waiting for format() response");
+    } catch (TimeoutException e) {
+      throw new IOException("Timed out waiting for format() response");
+    }
+    
+    if (call.countExceptions() > 0) {
+      call.rethrowException("Could not format one or more JournalNodes");
+    }
+  }
+
+  @Override
+  public boolean hasSomeData() throws IOException {
+    QuorumCall<AsyncLogger, Boolean> call =
+        loggers.isFormatted();
+
+    try {
+      call.waitFor(loggers.size(), 0, 0, HASDATA_TIMEOUT_MS, "hasSomeData");
+    } catch (InterruptedException e) {
+      throw new IOException("Interrupted while determining if JNs have data");
+    } catch (TimeoutException e) {
+      throw new IOException("Timed out waiting for response from loggers");
+    }
+    
+    if (call.countExceptions() > 0) {
+      call.rethrowException(
+          "Unable to check if JNs are ready for formatting");
+    }
+    
+    // If any of the loggers returned with a non-empty manifest, then
+    // we should prompt for format.
+    for (Boolean hasData : call.getResults().values()) {
+      if (hasData) {
+        return true;
+      }
+    }
+
+    // Otherwise, none were formatted, we can safely format.
+    return false;
+  }
+
+  /**
+   * Run recovery/synchronization for a specific segment.
+   * Postconditions:
+   * <ul>
+   * <li>This segment will be finalized on a majority
+   * of nodes.</li>
+   * <li>All nodes which contain the finalized segment will
+   * agree on the length.</li>
+   * </ul>
+   * 
+   * @param segmentTxId the starting txid of the segment
+   * @throws IOException
+   */
+  private void recoverUnclosedSegment(long segmentTxId) throws IOException {
+    Preconditions.checkArgument(segmentTxId > 0);
+    LOG.info("Beginning recovery of unclosed segment starting at txid " +
+        segmentTxId);
+    
+    // Step 1. Prepare recovery
+    QuorumCall<AsyncLogger,PrepareRecoveryResponseProto> prepare =
+        loggers.prepareRecovery(segmentTxId);
+    Map<AsyncLogger, PrepareRecoveryResponseProto> prepareResponses=
+        loggers.waitForWriteQuorum(prepare, prepareRecoveryTimeoutMs,
+            "prepareRecovery(" + segmentTxId + ")");
+    LOG.info("Recovery prepare phase complete. Responses:\n" +
+        QuorumCall.mapToString(prepareResponses));
+
+    // Determine the logger who either:
+    // a) Has already accepted a previous proposal that's higher than any
+    //    other
+    //
+    //  OR, if no such logger exists:
+    //
+    // b) Has the longest log starting at this transaction ID
+    
+    // TODO: we should collect any "ties" and pass the URL for all of them
+    // when syncing, so we can tolerate failure during recovery better.
+    Entry<AsyncLogger, PrepareRecoveryResponseProto> bestEntry = Collections.max(
+        prepareResponses.entrySet(), SegmentRecoveryComparator.INSTANCE); 
+    AsyncLogger bestLogger = bestEntry.getKey();
+    PrepareRecoveryResponseProto bestResponse = bestEntry.getValue();
+    
+    // Log the above decision, check invariants.
+    if (bestResponse.hasAcceptedInEpoch()) {
+      LOG.info("Using already-accepted recovery for segment " +
+          "starting at txid " + segmentTxId + ": " +
+          bestEntry);
+    } else if (bestResponse.hasSegmentState()) {
+      LOG.info("Using longest log: " + bestEntry);
+    } else {
+      // None of the responses to prepareRecovery() had a segment at the given
+      // txid. This can happen for example in the following situation:
+      // - 3 JNs: JN1, JN2, JN3
+      // - writer starts segment 101 on JN1, then crashes before
+      //   writing to JN2 and JN3
+      // - during newEpoch(), we saw the segment on JN1 and decide to
+      //   recover segment 101
+      // - before prepare(), JN1 crashes, and we only talk to JN2 and JN3,
+      //   neither of which has any entry for this log.
+      // In this case, it is allowed to do nothing for recovery, since the
+      // segment wasn't started on a quorum of nodes.
+
+      // Sanity check: we should only get here if none of the responses had
+      // a log. This should be a postcondition of the recovery comparator,
+      // but a bug in the comparator might cause us to get here.
+      for (PrepareRecoveryResponseProto resp : prepareResponses.values()) {
+        assert !resp.hasSegmentState() :
+          "One of the loggers had a response, but no best logger " +
+          "was found.";
+      }
+
+      LOG.info("None of the responders had a log to recover: " +
+          QuorumCall.mapToString(prepareResponses));
+      return;
+    }
+    
+    SegmentStateProto logToSync = bestResponse.getSegmentState();
+    assert segmentTxId == logToSync.getStartTxId();
+    
+    // Sanity check: none of the loggers should be aware of a higher
+    // txid than the txid we intend to truncate to
+    for (Map.Entry<AsyncLogger, PrepareRecoveryResponseProto> e :
+         prepareResponses.entrySet()) {
+      AsyncLogger logger = e.getKey();
+      PrepareRecoveryResponseProto resp = e.getValue();
+
+      if (resp.hasLastCommittedTxId() &&
+          resp.getLastCommittedTxId() > logToSync.getEndTxId()) {
+        throw new AssertionError("Decided to synchronize log to " + logToSync +
+            " but logger " + logger + " had seen txid " +
+            resp.getLastCommittedTxId() + " committed");
+      }
+    }
+    
+    URL syncFromUrl = bestLogger.buildURLToFetchLogs(segmentTxId);
+    
+    QuorumCall<AsyncLogger,Void> accept = loggers.acceptRecovery(logToSync, syncFromUrl);
+    loggers.waitForWriteQuorum(accept, acceptRecoveryTimeoutMs,
+        "acceptRecovery(" + TextFormat.shortDebugString(logToSync) + ")");
+
+    // If one of the loggers above missed the synchronization step above, but
+    // we send a finalize() here, that's OK. It validates the log before
+    // finalizing. Hence, even if it is not "in sync", it won't incorrectly
+    // finalize.
+    QuorumCall<AsyncLogger, Void> finalize =
+        loggers.finalizeLogSegment(logToSync.getStartTxId(), logToSync.getEndTxId()); 
+    loggers.waitForWriteQuorum(finalize, finalizeSegmentTimeoutMs,
+        String.format("finalizeLogSegment(%s-%s)",
+            logToSync.getStartTxId(),
+            logToSync.getEndTxId()));
+  }
+  
+  static List<AsyncLogger> createLoggers(Configuration conf,
+      URI uri, NamespaceInfo nsInfo, AsyncLogger.Factory factory)
+          throws IOException {
+    List<AsyncLogger> ret = Lists.newArrayList();
+    List<InetSocketAddress> addrs = getLoggerAddresses(uri);
+    String jid = parseJournalId(uri);
+    for (InetSocketAddress addr : addrs) {
+      ret.add(factory.createLogger(conf, nsInfo, jid, addr));
+    }
+    return ret;
+  }
+ 
+  private static List<InetSocketAddress> getLoggerAddresses(URI uri)
+      throws IOException {
+    String authority = uri.getAuthority();
+    Preconditions.checkArgument(authority != null && !authority.isEmpty(),
+        "URI has no authority: " + uri);
+    
+    String[] parts = StringUtils.split(authority, ';');
+    for (int i = 0; i < parts.length; i++) {
+      parts[i] = parts[i].trim();
+    }
+
+    if (parts.length % 2 == 0) {
+      LOG.warn("Quorum journal URI '" + uri + "' has an even number " +
+          "of Journal Nodes specified. This is not recommended!");
+    }
+    
+    List<InetSocketAddress> addrs = Lists.newArrayList();
+    for (String addr : parts) {
+      addrs.add(NetUtils.createSocketAddr(
+          addr, DFSConfigKeys.DFS_JOURNALNODE_RPC_PORT_DEFAULT));
+    }
+    return addrs;
+  }
+  
+  @Override
+  public EditLogOutputStream startLogSegment(long txId) throws IOException {
+    Preconditions.checkState(isActiveWriter,
+        "must recover segments before starting a new one");
+    QuorumCall<AsyncLogger,Void> q = loggers.startLogSegment(txId);
+    loggers.waitForWriteQuorum(q, startSegmentTimeoutMs,
+        "startLogSegment(" + txId + ")");
+    return new QuorumOutputStream(loggers, txId,
+        outputBufferCapacity, writeTxnsTimeoutMs);
+  }
+
+  @Override
+  public void finalizeLogSegment(long firstTxId, long lastTxId)
+      throws IOException {
+    QuorumCall<AsyncLogger,Void> q = loggers.finalizeLogSegment(
+        firstTxId, lastTxId);
+    loggers.waitForWriteQuorum(q, finalizeSegmentTimeoutMs,
+        String.format("finalizeLogSegment(%s-%s)", firstTxId, lastTxId));
+  }
+
+  @Override
+  public void setOutputBufferCapacity(int size) {
+    outputBufferCapacity = size;
+  }
+
+  @Override
+  public void purgeLogsOlderThan(long minTxIdToKeep) throws IOException {
+    // This purges asynchronously -- there's no need to wait for a quorum
+    // here, because it's always OK to fail.
+    LOG.info("Purging remote journals older than txid " + minTxIdToKeep);
+    loggers.purgeLogsOlderThan(minTxIdToKeep);
+  }
+
+  @Override
+  public void recoverUnfinalizedSegments() throws IOException {
+    Preconditions.checkState(!isActiveWriter, "already active writer");
+    
+    LOG.info("Starting recovery process for unclosed journal segments...");
+    Map<AsyncLogger, NewEpochResponseProto> resps = createNewUniqueEpoch();
+    LOG.info("Successfully started new epoch " + loggers.getEpoch());
+
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("newEpoch(" + loggers.getEpoch() + ") responses:\n" +
+        QuorumCall.mapToString(resps));
+    }
+    
+    long mostRecentSegmentTxId = Long.MIN_VALUE;
+    for (NewEpochResponseProto r : resps.values()) {
+      if (r.hasLastSegmentTxId()) {
+        mostRecentSegmentTxId = Math.max(mostRecentSegmentTxId,
+            r.getLastSegmentTxId());
+      }
+    }
+    
+    // On a completely fresh system, none of the journals have any
+    // segments, so there's nothing to recover.
+    if (mostRecentSegmentTxId != Long.MIN_VALUE) {
+      recoverUnclosedSegment(mostRecentSegmentTxId);
+    }
+    isActiveWriter = true;
+  }
+
+  @Override
+  public void close() throws IOException {
+    loggers.close();
+  }
+
+  @Override
+  public void selectInputStreams(Collection<EditLogInputStream> streams,
+      long fromTxnId, boolean inProgressOk) throws IOException {
+
+    QuorumCall<AsyncLogger, RemoteEditLogManifest> q =
+        loggers.getEditLogManifest(fromTxnId);
+    Map<AsyncLogger, RemoteEditLogManifest> resps =
+        loggers.waitForWriteQuorum(q, selectInputStreamsTimeoutMs,
+            "selectInputStreams");
+    
+    LOG.debug("selectInputStream manifests:\n" +
+        Joiner.on("\n").withKeyValueSeparator(": ").join(resps));
+    
+    final PriorityQueue<EditLogInputStream> allStreams = 
+        new PriorityQueue<EditLogInputStream>(64,
+            JournalSet.EDIT_LOG_INPUT_STREAM_COMPARATOR);
+    for (Map.Entry<AsyncLogger, RemoteEditLogManifest> e : resps.entrySet()) {
+      AsyncLogger logger = e.getKey();
+      RemoteEditLogManifest manifest = e.getValue();
+      
+      for (RemoteEditLog remoteLog : manifest.getLogs()) {
+        URL url = logger.buildURLToFetchLogs(remoteLog.getStartTxId());
+
+        EditLogInputStream elis = EditLogFileInputStream.fromUrl(
+            url, remoteLog.getStartTxId(), remoteLog.getEndTxId(),
+            remoteLog.isInProgress());
+        allStreams.add(elis);
+      }
+    }
+    JournalSet.chainAndMakeRedundantStreams(
+        streams, allStreams, fromTxnId, inProgressOk);
+  }
+  
+  @Override
+  public String toString() {
+    return "QJM to " + loggers;
+  }
+
+  @VisibleForTesting
+  AsyncLoggerSet getLoggerSetForTests() {
+    return loggers;
+  }
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumOutputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumOutputStream.java
new file mode 100644
index 0000000..7a9549d
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/QuorumOutputStream.java
@@ -0,0 +1,128 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream;
+import org.apache.hadoop.hdfs.server.namenode.EditsDoubleBuffer;
+import org.apache.hadoop.hdfs.server.namenode.FSEditLogOp;
+import org.apache.hadoop.io.DataOutputBuffer;
+
+/**
+ * EditLogOutputStream implementation that writes to a quorum of
+ * remote journals.
+ */
+class QuorumOutputStream extends EditLogOutputStream {
+  private final AsyncLoggerSet loggers;
+  private EditsDoubleBuffer buf;
+  private final long segmentTxId;
+  private final int writeTimeoutMs;
+
+  public QuorumOutputStream(AsyncLoggerSet loggers,
+      long txId, int outputBufferCapacity,
+      int writeTimeoutMs) throws IOException {
+    super();
+    this.buf = new EditsDoubleBuffer(outputBufferCapacity);
+    this.loggers = loggers;
+    this.segmentTxId = txId;
+    this.writeTimeoutMs = writeTimeoutMs;
+  }
+
+  @Override
+  public void write(FSEditLogOp op) throws IOException {
+    buf.writeOp(op);
+  }
+
+  @Override
+  public void writeRaw(byte[] bytes, int offset, int length) throws IOException {
+    buf.writeRaw(bytes, offset, length);
+  }
+
+  @Override
+  public void create() throws IOException {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public void close() throws IOException {
+    if (buf != null) {
+      buf.close();
+      buf = null;
+    }
+  }
+
+  @Override
+  public void abort() throws IOException {
+    QuorumJournalManager.LOG.warn("Aborting " + this);
+    buf = null;
+    close();
+  }
+
+  @Override
+  public void setReadyToFlush() throws IOException {
+    buf.setReadyToFlush();
+  }
+
+  @Override
+  protected void flushAndSync(boolean durable) throws IOException {
+    int numReadyBytes = buf.countReadyBytes();
+    if (numReadyBytes > 0) {
+      int numReadyTxns = buf.countReadyTxns();
+      long firstTxToFlush = buf.getFirstReadyTxId();
+
+      assert numReadyTxns > 0;
+
+      // Copy from our double-buffer into a new byte array. This is for
+      // two reasons:
+      // 1) The IPC code has no way of specifying to send only a slice of
+      //    a larger array.
+      // 2) because the calls to the underlying nodes are asynchronous, we
+      //    need a defensive copy to avoid accidentally mutating the buffer
+      //    before it is sent.
+      DataOutputBuffer bufToSend = new DataOutputBuffer(numReadyBytes);
+      buf.flushTo(bufToSend);
+      assert bufToSend.getLength() == numReadyBytes;
+      byte[] data = bufToSend.getData();
+      assert data.length == bufToSend.getLength();
+
+      QuorumCall<AsyncLogger, Void> qcall = loggers.sendEdits(
+          segmentTxId, firstTxToFlush,
+          numReadyTxns, data);
+      loggers.waitForWriteQuorum(qcall, writeTimeoutMs, "sendEdits");
+      
+      // Since we successfully wrote this batch, let the loggers know. Any future
+      // RPCs will thus let the loggers know of the most recent transaction, even
+      // if a logger has fallen behind.
+      loggers.setCommittedTxId(firstTxToFlush + numReadyTxns - 1);
+    }
+  }
+
+  @Override
+  public String generateHtmlReport() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("Writing segment beginning at txid " + segmentTxId + "<br/>\n");
+    loggers.appendHtmlReport(sb);
+    return sb.toString();
+  }
+  
+  @Override
+  public String toString() {
+    return "QuorumOutputStream starting at txid " + segmentTxId;
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/SegmentRecoveryComparator.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/SegmentRecoveryComparator.java
new file mode 100644
index 0000000..61b60aa
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/SegmentRecoveryComparator.java
@@ -0,0 +1,91 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import java.util.Comparator;
+import java.util.Map.Entry;
+
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ComparisonChain;
+import com.google.common.primitives.Booleans;
+
+/**
+ * Compares responses to the prepareRecovery RPC. This is responsible for
+ * determining the correct length to recover.
+ */
+class SegmentRecoveryComparator
+    implements Comparator<Entry<AsyncLogger, PrepareRecoveryResponseProto>> {
+
+  static final SegmentRecoveryComparator INSTANCE = new SegmentRecoveryComparator();
+  
+  @Override
+  public int compare(
+      Entry<AsyncLogger, PrepareRecoveryResponseProto> a,
+      Entry<AsyncLogger, PrepareRecoveryResponseProto> b) {
+    
+    PrepareRecoveryResponseProto r1 = a.getValue();
+    PrepareRecoveryResponseProto r2 = b.getValue();
+    
+    // A response that has data for a segment is always better than one
+    // that doesn't.
+    if (r1.hasSegmentState() != r2.hasSegmentState()) {
+      return Booleans.compare(r1.hasSegmentState(), r2.hasSegmentState());
+    }
+    
+    if (!r1.hasSegmentState()) {
+      // Neither has a segment, so neither can be used for recover.
+      // Call them equal.
+      return 0;
+    }
+    
+    // They both have a segment.
+    SegmentStateProto r1Seg = r1.getSegmentState();
+    SegmentStateProto r2Seg = r2.getSegmentState();
+    
+    Preconditions.checkArgument(r1Seg.getStartTxId() == r2Seg.getStartTxId(),
+        "Should only be called with responses for corresponding segments: " +
+        "%s and %s do not have the same start txid.", r1, r2);
+
+    // If one is in-progress but the other is finalized,
+    // the finalized one is greater.
+    if (r1Seg.getIsInProgress() != r2Seg.getIsInProgress()) {
+      return Booleans.compare(!r1Seg.getIsInProgress(), !r2Seg.getIsInProgress());
+    }
+    
+    if (!r1Seg.getIsInProgress()) {
+      // If both are finalized, they should match lengths
+      if (r1Seg.getEndTxId() != r2Seg.getEndTxId()) {
+        throw new AssertionError("finalized segs with different lengths: " + 
+            r1 + ", " + r2);
+      }
+      return 0;
+    }
+    
+    // Both are in-progress.
+    long r1SeenEpoch = Math.max(r1.getAcceptedInEpoch(), r1.getLastWriterEpoch());
+    long r2SeenEpoch = Math.max(r2.getAcceptedInEpoch(), r2.getLastWriterEpoch());
+    
+    return ComparisonChain.start()
+        .compare(r1SeenEpoch, r2SeenEpoch)
+        .compare(r1.getSegmentState().getEndTxId(), r2.getSegmentState().getEndTxId())
+        .result();
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/JournalNotFormattedException.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/JournalNotFormattedException.java
new file mode 100644
index 0000000..874d648
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/JournalNotFormattedException.java
@@ -0,0 +1,35 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.protocol;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import java.io.IOException;
+
+/**
+ * Exception indicating that a call has been made to a JournalNode
+ * which is not yet formatted.
+ */
+@InterfaceAudience.Private
+public class JournalNotFormattedException extends IOException {
+  private static final long serialVersionUID = 1L;
+  
+  public JournalNotFormattedException(String msg) {
+    super(msg);
+  }
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/JournalOutOfSyncException.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/JournalOutOfSyncException.java
new file mode 100644
index 0000000..15a972c
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/JournalOutOfSyncException.java
@@ -0,0 +1,32 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.protocol;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class JournalOutOfSyncException extends IOException {
+  private static final long serialVersionUID = 1L;
+  
+  public JournalOutOfSyncException(String msg) {
+    super(msg);
+  }
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/QJournalProtocol.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/QJournalProtocol.java
new file mode 100644
index 0000000..769d084
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/QJournalProtocol.java
@@ -0,0 +1,143 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.protocol;
+
+import java.io.IOException;
+import java.net.URL;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetEditLogManifestResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.qjournal.server.JournalNode;
+import org.apache.hadoop.hdfs.server.namenode.JournalManager;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.security.KerberosInfo;
+
+/**
+ * Protocol used to communicate between {@link QuorumJournalManager}
+ * and each {@link JournalNode}.
+ * 
+ * This is responsible for sending edits as well as coordinating
+ * recovery of the nodes.
+ */
+@KerberosInfo(
+    serverPrincipal = DFSConfigKeys.DFS_JOURNALNODE_USER_NAME_KEY,
+    clientPrincipal = DFSConfigKeys.DFS_NAMENODE_USER_NAME_KEY)
+@InterfaceAudience.Private
+public interface QJournalProtocol {
+  public static final long versionID = 1L;
+
+  /**
+   * @return true if the given journal has been formatted and
+   * contains valid data.
+   */
+  public boolean isFormatted(String journalId) throws IOException;
+
+  /**
+   * Get the current state of the journal, including the most recent
+   * epoch number and the HTTP port.
+   */
+  public GetJournalStateResponseProto getJournalState(String journalId)
+      throws IOException;
+  
+  /**
+   * Format the underlying storage for the given namespace.
+   */
+  public void format(String journalId,
+      NamespaceInfo nsInfo) throws IOException;
+
+  /**
+   * Begin a new epoch. See the HDFS-3077 design doc for details.
+   */
+  public NewEpochResponseProto newEpoch(String journalId,
+      NamespaceInfo nsInfo, long epoch) throws IOException;
+  
+  /**
+   * Journal edit records.
+   * This message is sent by the active name-node to the JournalNodes
+   * to write edits to their local logs.
+   */
+  public void journal(RequestInfo reqInfo,
+                      long segmentTxId,
+                      long firstTxnId,
+                      int numTxns,
+                      byte[] records) throws IOException;
+
+  
+  /**
+   * Heartbeat.
+   * This is a no-op on the server, except that it verifies that the
+   * caller is in fact still the active writer, and provides up-to-date
+   * information on the most recently committed txid.
+   */
+  public void heartbeat(RequestInfo reqInfo) throws IOException;
+  
+  /**
+   * Start writing to a new log segment on the JournalNode.
+   * Before calling this, one should finalize the previous segment
+   * using {@link #finalizeLogSegment(RequestInfo, long, long)}.
+   * 
+   * @param txid the first txid in the new log
+   */
+  public void startLogSegment(RequestInfo reqInfo,
+      long txid) throws IOException;
+
+  /**
+   * Finalize the given log segment on the JournalNode. The segment
+   * is expected to be in-progress and starting at the given startTxId.
+   *
+   * @param startTxId the starting transaction ID of the log
+   * @param endTxId the expected last transaction in the given log
+   * @throws IOException if no such segment exists
+   */
+  public void finalizeLogSegment(RequestInfo reqInfo,
+      long startTxId, long endTxId) throws IOException;
+
+  /**
+   * @throws IOException 
+   * @see JournalManager#purgeLogsOlderThan(long)
+   */
+  public void purgeLogsOlderThan(RequestInfo requestInfo, long minTxIdToKeep)
+      throws IOException;
+  
+  /**
+   * @param jid the journal from which to enumerate edits
+   * @param sinceTxId the first transaction which the client cares about
+   * @return a list of edit log segments since the given transaction ID.
+   */
+  public GetEditLogManifestResponseProto getEditLogManifest(
+      String jid, long sinceTxId) throws IOException;
+  
+  /**
+   * Begin the recovery process for a given segment. See the HDFS-3077
+   * design document for details.
+   */
+  public PrepareRecoveryResponseProto prepareRecovery(RequestInfo reqInfo,
+      long segmentTxId) throws IOException;
+
+  /**
+   * Accept a proposed recovery for the given transaction ID.
+   */
+  public void acceptRecovery(RequestInfo reqInfo,
+      SegmentStateProto stateToAccept, URL fromUrl) throws IOException;
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/RequestInfo.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/RequestInfo.java
new file mode 100644
index 0000000..b2167a5
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocol/RequestInfo.java
@@ -0,0 +1,65 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.protocol;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hdfs.protocol.HdfsConstants;
+
+@InterfaceAudience.Private
+public class RequestInfo {
+  private String jid;
+  private long epoch;
+  private long ipcSerialNumber;
+  private long committedTxId;
+  
+  public RequestInfo(String jid, long epoch, long ipcSerialNumber,
+      long committedTxId) {
+    this.jid = jid;
+    this.epoch = epoch;
+    this.ipcSerialNumber = ipcSerialNumber;
+    this.committedTxId = committedTxId;
+  }
+
+  public long getEpoch() {
+    return epoch;
+  }
+
+  public void setEpoch(long epoch) {
+    this.epoch = epoch;
+  }
+  
+  public String getJournalId() {
+    return jid;
+  }
+
+  public long getIpcSerialNumber() {
+    return ipcSerialNumber;
+  }
+
+  public void setIpcSerialNumber(long ipcSerialNumber) {
+    this.ipcSerialNumber = ipcSerialNumber;
+  }
+
+  public long getCommittedTxId() {
+    return committedTxId;
+  }
+
+  public boolean hasCommittedTxId() {
+    return (committedTxId != HdfsConstants.INVALID_TXID);
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolPB.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolPB.java
new file mode 100644
index 0000000..240bbfb
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolPB.java
@@ -0,0 +1,41 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.protocolPB;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.QJournalProtocolService;
+import org.apache.hadoop.ipc.ProtocolInfo;
+import org.apache.hadoop.security.KerberosInfo;
+
+/**
+ * Protocol used to journal edits to a JournalNode participating
+ * in the quorum journal.
+ * Note: This extends the protocolbuffer service based interface to
+ * add annotations required for security.
+ */
+@KerberosInfo(
+    serverPrincipal = DFSConfigKeys.DFS_JOURNALNODE_USER_NAME_KEY,
+    clientPrincipal = DFSConfigKeys.DFS_NAMENODE_USER_NAME_KEY)
+@ProtocolInfo(protocolName = 
+    "org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol",
+    protocolVersion = 1)
+@InterfaceAudience.Private
+public interface QJournalProtocolPB extends
+    QJournalProtocolService.BlockingInterface {
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolServerSideTranslatorPB.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolServerSideTranslatorPB.java
new file mode 100644
index 0000000..a232331
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolServerSideTranslatorPB.java
@@ -0,0 +1,239 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.protocolPB;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hdfs.protocol.HdfsConstants;
+import org.apache.hadoop.hdfs.protocolPB.PBHelper;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.FinalizeLogSegmentRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.FinalizeLogSegmentResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.FormatRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.FormatResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetEditLogManifestRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetEditLogManifestResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.HeartbeatRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.HeartbeatResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.IsFormattedRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.IsFormattedResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.JournalIdProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.JournalRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.JournalResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.AcceptRecoveryRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.AcceptRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PurgeLogsRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PurgeLogsResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.StartLogSegmentRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.StartLogSegmentResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
+
+import com.google.protobuf.RpcController;
+import com.google.protobuf.ServiceException;
+
+import java.io.IOException;
+import java.net.URL;
+
+/**
+ * Implementation for protobuf service that forwards requests
+ * received on {@link JournalProtocolPB} to the 
+ * {@link JournalProtocol} server implementation.
+ */
+@InterfaceAudience.Private
+public class QJournalProtocolServerSideTranslatorPB implements QJournalProtocolPB {
+  /** Server side implementation to delegate the requests to */
+  private final QJournalProtocol impl;
+
+  public QJournalProtocolServerSideTranslatorPB(QJournalProtocol impl) {
+    this.impl = impl;
+  }
+
+  
+  @Override
+  public IsFormattedResponseProto isFormatted(RpcController controller,
+      IsFormattedRequestProto request) throws ServiceException {
+    try {
+      boolean ret = impl.isFormatted(
+          convert(request.getJid()));
+      return IsFormattedResponseProto.newBuilder()
+          .setIsFormatted(ret)
+          .build();
+    } catch (IOException ioe) {
+      throw new ServiceException(ioe);
+    }
+  }
+
+
+  @Override
+  public GetJournalStateResponseProto getJournalState(RpcController controller,
+      GetJournalStateRequestProto request) throws ServiceException {
+    try {
+      return impl.getJournalState(
+          convert(request.getJid()));
+    } catch (IOException ioe) {
+      throw new ServiceException(ioe);
+    }
+  }
+
+  private String convert(JournalIdProto jid) {
+    return jid.getIdentifier();
+  }
+
+  @Override
+  public NewEpochResponseProto newEpoch(RpcController controller,
+      NewEpochRequestProto request) throws ServiceException {
+    try {
+      return impl.newEpoch(
+          request.getJid().getIdentifier(),
+          PBHelper.convert(request.getNsInfo()),
+          request.getEpoch());
+    } catch (IOException ioe) {
+      throw new ServiceException(ioe);
+    }
+  }
+
+  public FormatResponseProto format(RpcController controller,
+      FormatRequestProto request) throws ServiceException {
+    try {
+      impl.format(request.getJid().getIdentifier(),
+          PBHelper.convert(request.getNsInfo()));
+      return FormatResponseProto.getDefaultInstance();
+    } catch (IOException ioe) {
+      throw new ServiceException(ioe);
+    }
+  }
+  
+  /** @see JournalProtocol#journal */
+  @Override
+  public JournalResponseProto journal(RpcController unused,
+      JournalRequestProto req) throws ServiceException {
+    try {
+      impl.journal(convert(req.getReqInfo()),
+          req.getSegmentTxnId(), req.getFirstTxnId(),
+          req.getNumTxns(), req.getRecords().toByteArray());
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+    return JournalResponseProto.newBuilder().build();
+  }
+
+  /** @see JournalProtocol#heartbeat */
+  @Override
+  public HeartbeatResponseProto heartbeat(RpcController controller,
+      HeartbeatRequestProto req) throws ServiceException {
+    try {
+      impl.heartbeat(convert(req.getReqInfo()));
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+    return HeartbeatResponseProto.getDefaultInstance();
+  }
+
+  /** @see JournalProtocol#startLogSegment */
+  @Override
+  public StartLogSegmentResponseProto startLogSegment(RpcController controller,
+      StartLogSegmentRequestProto req) throws ServiceException {
+    try {
+      impl.startLogSegment(convert(req.getReqInfo()),
+          req.getTxid());
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+    return StartLogSegmentResponseProto.newBuilder().build();
+  }
+  
+  @Override
+  public FinalizeLogSegmentResponseProto finalizeLogSegment(
+      RpcController controller, FinalizeLogSegmentRequestProto req)
+      throws ServiceException {
+    try {
+      impl.finalizeLogSegment(convert(req.getReqInfo()),
+          req.getStartTxId(), req.getEndTxId());
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+    return FinalizeLogSegmentResponseProto.newBuilder().build();
+  }
+  
+  @Override
+  public PurgeLogsResponseProto purgeLogs(RpcController controller,
+      PurgeLogsRequestProto req) throws ServiceException {
+    try {
+      impl.purgeLogsOlderThan(convert(req.getReqInfo()),
+          req.getMinTxIdToKeep());
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+    return PurgeLogsResponseProto.getDefaultInstance();
+  }
+
+  @Override
+  public GetEditLogManifestResponseProto getEditLogManifest(
+      RpcController controller, GetEditLogManifestRequestProto request)
+      throws ServiceException {
+    try {
+      return impl.getEditLogManifest(
+          request.getJid().getIdentifier(),
+          request.getSinceTxId());
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
+
+
+  @Override
+  public PrepareRecoveryResponseProto prepareRecovery(RpcController controller,
+      PrepareRecoveryRequestProto request) throws ServiceException {
+    try {
+      return impl.prepareRecovery(convert(request.getReqInfo()),
+          request.getSegmentTxId());
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
+
+  @Override
+  public AcceptRecoveryResponseProto acceptRecovery(RpcController controller,
+      AcceptRecoveryRequestProto request) throws ServiceException {
+    try {
+      impl.acceptRecovery(convert(request.getReqInfo()),
+          request.getStateToAccept(),
+          new URL(request.getFromURL()));
+      return AcceptRecoveryResponseProto.getDefaultInstance();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
+
+  
+  private RequestInfo convert(
+      QJournalProtocolProtos.RequestInfoProto reqInfo) {
+    return new RequestInfo(
+        reqInfo.getJournalId().getIdentifier(),
+        reqInfo.getEpoch(),
+        reqInfo.getIpcSerialNumber(),
+        reqInfo.hasCommittedTxId() ?
+          reqInfo.getCommittedTxId() : HdfsConstants.INVALID_TXID);
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolTranslatorPB.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolTranslatorPB.java
new file mode 100644
index 0000000..290a62a
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/protocolPB/QJournalProtocolTranslatorPB.java
@@ -0,0 +1,278 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.protocolPB;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.net.URL;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.protocolPB.PBHelper;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.FinalizeLogSegmentRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.FormatRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetEditLogManifestRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetEditLogManifestResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.HeartbeatRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.IsFormattedRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.IsFormattedResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.JournalIdProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.JournalRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.AcceptRecoveryRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PurgeLogsRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.RequestInfoProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.StartLogSegmentRequestProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
+import org.apache.hadoop.hdfs.server.protocol.JournalProtocol;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.ipc.ProtobufHelper;
+import org.apache.hadoop.ipc.ProtocolMetaInterface;
+import org.apache.hadoop.ipc.RPC;
+import org.apache.hadoop.ipc.RpcClientUtil;
+
+import com.google.protobuf.RpcController;
+import com.google.protobuf.ServiceException;
+
+/**
+ * This class is the client side translator to translate the requests made on
+ * {@link JournalProtocol} interfaces to the RPC server implementing
+ * {@link JournalProtocolPB}.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Stable
+public class QJournalProtocolTranslatorPB implements ProtocolMetaInterface,
+    QJournalProtocol, Closeable {
+  /** RpcController is not used and hence is set to null */
+  private final static RpcController NULL_CONTROLLER = null;
+  private final QJournalProtocolPB rpcProxy;
+  
+  public QJournalProtocolTranslatorPB(QJournalProtocolPB rpcProxy) {
+    this.rpcProxy = rpcProxy;
+  }
+
+  @Override
+  public void close() {
+    RPC.stopProxy(rpcProxy);
+  }
+
+
+  @Override
+  public boolean isFormatted(String journalId) throws IOException {
+    try {
+      IsFormattedRequestProto req = IsFormattedRequestProto.newBuilder()
+          .setJid(convertJournalId(journalId))
+          .build();
+      IsFormattedResponseProto resp = rpcProxy.isFormatted(
+          NULL_CONTROLLER, req);
+      return resp.getIsFormatted();
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  @Override
+  public GetJournalStateResponseProto getJournalState(String jid)
+      throws IOException {
+    try {
+      GetJournalStateRequestProto req = GetJournalStateRequestProto.newBuilder()
+          .setJid(convertJournalId(jid))
+          .build();
+      return rpcProxy.getJournalState(NULL_CONTROLLER, req);
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  private JournalIdProto convertJournalId(String jid) {
+    return JournalIdProto.newBuilder()
+        .setIdentifier(jid)
+        .build();
+  }
+  
+  @Override
+  public void format(String jid, NamespaceInfo nsInfo) throws IOException {
+    try {
+      FormatRequestProto req = FormatRequestProto.newBuilder()
+          .setJid(convertJournalId(jid))
+          .setNsInfo(PBHelper.convert(nsInfo))
+          .build();
+      rpcProxy.format(NULL_CONTROLLER, req);
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  @Override
+  public NewEpochResponseProto newEpoch(String jid, NamespaceInfo nsInfo,
+      long epoch) throws IOException {
+    try {
+      NewEpochRequestProto req = NewEpochRequestProto.newBuilder()
+        .setJid(convertJournalId(jid))
+        .setNsInfo(PBHelper.convert(nsInfo))
+        .setEpoch(epoch)
+        .build();
+      return rpcProxy.newEpoch(NULL_CONTROLLER, req);
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  @Override
+  public void journal(RequestInfo reqInfo,
+      long segmentTxId, long firstTxnId, int numTxns,
+      byte[] records) throws IOException {
+    JournalRequestProto req = JournalRequestProto.newBuilder()
+        .setReqInfo(convert(reqInfo))
+        .setSegmentTxnId(segmentTxId)
+        .setFirstTxnId(firstTxnId)
+        .setNumTxns(numTxns)
+        .setRecords(PBHelper.getByteString(records))
+        .build();
+    try {
+      rpcProxy.journal(NULL_CONTROLLER, req);
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+  
+  @Override
+  public void heartbeat(RequestInfo reqInfo) throws IOException {
+    try {
+      rpcProxy.heartbeat(NULL_CONTROLLER, HeartbeatRequestProto.newBuilder()
+            .setReqInfo(convert(reqInfo))
+            .build());
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  private QJournalProtocolProtos.RequestInfoProto convert(
+      RequestInfo reqInfo) {
+    RequestInfoProto.Builder builder = RequestInfoProto.newBuilder()
+        .setJournalId(convertJournalId(reqInfo.getJournalId()))
+        .setEpoch(reqInfo.getEpoch())
+        .setIpcSerialNumber(reqInfo.getIpcSerialNumber());
+    if (reqInfo.hasCommittedTxId()) {
+      builder.setCommittedTxId(reqInfo.getCommittedTxId());
+    }
+    return builder.build();
+  }
+
+  @Override
+  public void startLogSegment(RequestInfo reqInfo, long txid)
+      throws IOException {
+    StartLogSegmentRequestProto req = StartLogSegmentRequestProto.newBuilder()
+        .setReqInfo(convert(reqInfo))
+        .setTxid(txid)
+        .build();
+    try {
+      rpcProxy.startLogSegment(NULL_CONTROLLER, req);
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+  
+  @Override
+  public void finalizeLogSegment(RequestInfo reqInfo, long startTxId,
+      long endTxId) throws IOException {
+    FinalizeLogSegmentRequestProto req =
+        FinalizeLogSegmentRequestProto.newBuilder()
+        .setReqInfo(convert(reqInfo))
+        .setStartTxId(startTxId)
+        .setEndTxId(endTxId)
+        .build();
+    try {
+      rpcProxy.finalizeLogSegment(NULL_CONTROLLER, req);
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+  
+  @Override
+  public void purgeLogsOlderThan(RequestInfo reqInfo, long minTxIdToKeep)
+      throws IOException {
+    PurgeLogsRequestProto req = PurgeLogsRequestProto.newBuilder()
+        .setReqInfo(convert(reqInfo))
+        .setMinTxIdToKeep(minTxIdToKeep)
+        .build();
+    try {
+      rpcProxy.purgeLogs(NULL_CONTROLLER, req);
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  @Override
+  public GetEditLogManifestResponseProto getEditLogManifest(String jid,
+      long sinceTxId) throws IOException {
+    try {
+      return rpcProxy.getEditLogManifest(NULL_CONTROLLER,
+          GetEditLogManifestRequestProto.newBuilder()
+            .setJid(convertJournalId(jid))
+            .setSinceTxId(sinceTxId)
+            .build());
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  @Override
+  public PrepareRecoveryResponseProto prepareRecovery(RequestInfo reqInfo,
+      long segmentTxId) throws IOException {
+    try {
+      return rpcProxy.prepareRecovery(NULL_CONTROLLER,
+          PrepareRecoveryRequestProto.newBuilder()
+            .setReqInfo(convert(reqInfo))
+            .setSegmentTxId(segmentTxId)
+            .build());
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  @Override
+  public void acceptRecovery(RequestInfo reqInfo,
+      SegmentStateProto stateToAccept, URL fromUrl) throws IOException {
+    try {
+      rpcProxy.acceptRecovery(NULL_CONTROLLER,
+          AcceptRecoveryRequestProto.newBuilder()
+            .setReqInfo(convert(reqInfo))
+            .setStateToAccept(stateToAccept)
+            .setFromURL(fromUrl.toExternalForm())
+            .build());
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  public boolean isMethodSupported(String methodName) throws IOException {
+    return RpcClientUtil.isMethodSupported(rpcProxy,
+        QJournalProtocolPB.class, RPC.RpcKind.RPC_PROTOCOL_BUFFER,
+        RPC.getProtocolVersion(QJournalProtocolPB.class), methodName);
+  }
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/GetJournalEditServlet.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/GetJournalEditServlet.java
new file mode 100644
index 0000000..6fac6a0
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/GetJournalEditServlet.java
@@ -0,0 +1,234 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.UnsupportedEncodingException;
+import java.net.URLEncoder;
+import java.util.HashSet;
+import java.util.Set;
+
+import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.DFSUtil;
+import org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager;
+import org.apache.hadoop.hdfs.server.common.JspHelper;
+import org.apache.hadoop.hdfs.server.namenode.FileJournalManager;
+import org.apache.hadoop.hdfs.server.namenode.FileJournalManager.EditLogFile;
+import org.apache.hadoop.hdfs.server.namenode.GetImageServlet;
+import org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode;
+import org.apache.hadoop.hdfs.server.namenode.TransferFsImage;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.util.DataTransferThrottler;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.security.SecurityUtil;
+import org.apache.hadoop.security.UserGroupInformation;
+import org.apache.hadoop.util.ServletUtil;
+import org.apache.hadoop.util.StringUtils;
+
+/**
+ * This servlet is used in two cases:
+ * <ul>
+ * <li>The QuorumJournalManager, when reading edits, fetches the edit streams
+ * from the journal nodes.</li>
+ * <li>During edits synchronization, one journal node will fetch edits from
+ * another journal node.</li>
+ * </ul>
+ */
+@InterfaceAudience.Private
+public class GetJournalEditServlet extends HttpServlet {
+
+  private static final long serialVersionUID = -4635891628211723009L;
+  private static final Log LOG = LogFactory.getLog(GetJournalEditServlet.class);
+
+  static final String STORAGEINFO_PARAM = "storageInfo";
+  static final String JOURNAL_ID_PARAM = "jid";
+  static final String SEGMENT_TXID_PARAM = "segmentTxId";
+
+  protected boolean isValidRequestor(HttpServletRequest request, Configuration conf)
+      throws IOException {
+    String remotePrincipal = request.getUserPrincipal().getName();
+    String remoteShortName = request.getRemoteUser();
+    if (remotePrincipal == null) { // This really shouldn't happen...
+      LOG.warn("Received null remoteUser while authorizing access to " +
+          "GetJournalEditServlet");
+      return false;
+    }
+
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("Validating request made by " + remotePrincipal +
+          " / " + remoteShortName + ". This user is: " +
+          UserGroupInformation.getLoginUser());
+    }
+
+    Set<String> validRequestors = new HashSet<String>();
+    validRequestors.addAll(DFSUtil.getAllNnPrincipals(conf));
+    validRequestors.add(
+        SecurityUtil.getServerPrincipal(conf
+            .get(DFSConfigKeys.DFS_SECONDARY_NAMENODE_USER_NAME_KEY),
+            SecondaryNameNode.getHttpAddress(conf).getHostName()));
+
+    // Check the full principal name of all the configured valid requestors.
+    for (String v : validRequestors) {
+      if (LOG.isDebugEnabled())
+        LOG.debug("isValidRequestor is comparing to valid requestor: " + v);
+      if (v != null && v.equals(remotePrincipal)) {
+        if (LOG.isDebugEnabled())
+          LOG.debug("isValidRequestor is allowing: " + remotePrincipal);
+        return true;
+      }
+    }
+
+    // Additionally, we compare the short name of the requestor to this JN's
+    // username, because we want to allow requests from other JNs during
+    // recovery, but we can't enumerate the full list of JNs.
+    if (remoteShortName.equals(
+          UserGroupInformation.getLoginUser().getShortUserName())) {
+      if (LOG.isDebugEnabled())
+        LOG.debug("isValidRequestor is allowing other JN principal: " +
+            remotePrincipal);
+      return true;
+    }
+
+    if (LOG.isDebugEnabled())
+      LOG.debug("isValidRequestor is rejecting: " + remotePrincipal);
+    return false;
+  }
+  
+  private boolean checkRequestorOrSendError(Configuration conf,
+      HttpServletRequest request, HttpServletResponse response)
+          throws IOException {
+    if (UserGroupInformation.isSecurityEnabled()
+        && !isValidRequestor(request, conf)) {
+      response.sendError(HttpServletResponse.SC_FORBIDDEN,
+          "Only Namenode and another JournalNode may access this servlet");
+      LOG.warn("Received non-NN/JN request for edits from "
+          + request.getRemoteHost());
+      return false;
+    }
+    return true;
+  }
+  
+  private boolean checkStorageInfoOrSendError(JNStorage storage,
+      HttpServletRequest request, HttpServletResponse response)
+      throws IOException {
+    String myStorageInfoString = storage.toColonSeparatedString();
+    String theirStorageInfoString = request.getParameter(STORAGEINFO_PARAM);
+    
+    if (theirStorageInfoString != null
+        && !myStorageInfoString.equals(theirStorageInfoString)) {
+      String msg = "This node has storage info '" + myStorageInfoString
+          + "' but the requesting node expected '"
+          + theirStorageInfoString + "'";
+      
+      response.sendError(HttpServletResponse.SC_FORBIDDEN, msg);
+      LOG.warn("Received an invalid request file transfer request from " +
+          request.getRemoteAddr() + ": " + msg);
+      return false;
+    }
+    return true;
+  }
+  
+  @Override
+  public void doGet(final HttpServletRequest request,
+      final HttpServletResponse response) throws ServletException, IOException {
+    FileInputStream editFileIn = null;
+    try {
+      final ServletContext context = getServletContext();
+      final Configuration conf = (Configuration) getServletContext()
+          .getAttribute(JspHelper.CURRENT_CONF);
+      final String journalId = request.getParameter(JOURNAL_ID_PARAM);
+      QuorumJournalManager.checkJournalId(journalId);
+      final JNStorage storage = JournalNodeHttpServer
+          .getJournalFromContext(context, journalId).getStorage();
+
+      // Check security
+      if (!checkRequestorOrSendError(conf, request, response)) {
+        return;
+      }
+
+      // Check that the namespace info is correct
+      if (!checkStorageInfoOrSendError(storage, request, response)) {
+        return;
+      }
+      
+      long segmentTxId = ServletUtil.parseLongParam(request,
+          SEGMENT_TXID_PARAM);
+
+      FileJournalManager fjm = storage.getJournalManager();
+      File editFile;
+
+      synchronized (fjm) {
+        // Synchronize on the FJM so that the file doesn't get finalized
+        // out from underneath us while we're in the process of opening
+        // it up.
+        EditLogFile elf = fjm.getLogFile(
+            segmentTxId);
+        if (elf == null) {
+          response.sendError(HttpServletResponse.SC_NOT_FOUND,
+              "No edit log found starting at txid " + segmentTxId);
+          return;
+        }
+        editFile = elf.getFile();
+        GetImageServlet.setVerificationHeaders(response, editFile);
+        GetImageServlet.setFileNameHeaders(response, editFile);
+        editFileIn = new FileInputStream(editFile);
+      }
+      
+      DataTransferThrottler throttler = GetImageServlet.getThrottler(conf);
+
+      // send edits
+      TransferFsImage.getFileServer(response, editFile, editFileIn, throttler);
+
+    } catch (Throwable t) {
+      String errMsg = "getedit failed. " + StringUtils.stringifyException(t);
+      response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, errMsg);
+      throw new IOException(errMsg);
+    } finally {
+      IOUtils.closeStream(editFileIn);
+    }
+  }
+
+  public static String buildPath(String journalId, long segmentTxId,
+      NamespaceInfo nsInfo) {
+    StringBuilder path = new StringBuilder("/getJournal?");
+    try {
+      path.append(JOURNAL_ID_PARAM).append("=")
+          .append(URLEncoder.encode(journalId, "UTF-8"));
+      path.append("&" + SEGMENT_TXID_PARAM).append("=")
+          .append(segmentTxId);
+      path.append("&" + STORAGEINFO_PARAM).append("=")
+          .append(URLEncoder.encode(nsInfo.toColonSeparatedString(), "UTF-8"));
+    } catch (UnsupportedEncodingException e) {
+      // Never get here -- everyone supports UTF-8
+      throw new RuntimeException(e);
+    }
+    return path.toString();
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JNStorage.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JNStorage.java
new file mode 100644
index 0000000..bb28e62
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JNStorage.java
@@ -0,0 +1,221 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import org.apache.hadoop.fs.FileUtil;
+import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.NodeType;
+import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.StartupOption;
+import org.apache.hadoop.hdfs.server.common.Storage;
+import org.apache.hadoop.hdfs.server.common.StorageErrorReporter;
+import org.apache.hadoop.hdfs.server.namenode.FileJournalManager;
+import org.apache.hadoop.hdfs.server.namenode.NNStorage;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+
+import com.google.common.collect.ImmutableList;
+
+/**
+ * A {@link Storage} implementation for the {@link JournalNode}.
+ * 
+ * The JN has a storage directory for each namespace for which it stores
+ * metadata. There is only a single directory per JN in the current design.
+ */
+class JNStorage extends Storage {
+
+  private final FileJournalManager fjm;
+  private final StorageDirectory sd;
+  private StorageState state;
+  
+
+  private static final List<Pattern> CURRENT_DIR_PURGE_REGEXES =
+      ImmutableList.of(
+        Pattern.compile("edits_\\d+-(\\d+)"),
+        Pattern.compile("edits_inprogress_(\\d+)(?:\\..*)?"));
+  
+  private static final List<Pattern> PAXOS_DIR_PURGE_REGEXES = 
+      ImmutableList.of(Pattern.compile("(\\d+)"));
+
+  /**
+   * @param logDir the path to the directory in which data will be stored
+   * @param errorReporter a callback to report errors
+   * @throws IOException 
+   */
+  protected JNStorage(File logDir, StorageErrorReporter errorReporter) throws IOException {
+    super(NodeType.JOURNAL_NODE);
+    
+    sd = new StorageDirectory(logDir);
+    this.addStorageDir(sd);
+    this.fjm = new FileJournalManager(sd, errorReporter);
+    
+    analyzeStorage();
+  }
+  
+  FileJournalManager getJournalManager() {
+    return fjm;
+  }
+
+  @Override
+  public boolean isPreUpgradableLayout(StorageDirectory sd) throws IOException {
+    return false;
+  }
+
+  /**
+   * Find an edits file spanning the given transaction ID range.
+   * If no such file exists, an exception is thrown.
+   */
+  File findFinalizedEditsFile(long startTxId, long endTxId) throws IOException {
+    File ret = new File(sd.getCurrentDir(),
+        NNStorage.getFinalizedEditsFileName(startTxId, endTxId));
+    if (!ret.exists()) {
+      throw new IOException(
+          "No edits file for range " + startTxId + "-" + endTxId);
+    }
+    return ret;
+  }
+
+  /**
+   * @return the path for an in-progress edits file starting at the given
+   * transaction ID. This does not verify existence of the file. 
+   */
+  File getInProgressEditLog(long startTxId) {
+    return new File(sd.getCurrentDir(),
+        NNStorage.getInProgressEditsFileName(startTxId));
+  }
+  
+  /**
+   * @param segmentTxId the first txid of the segment
+   * @param epoch the epoch number of the writer which is coordinating
+   * recovery
+   * @return the temporary path in which an edits log should be stored
+   * while it is being downloaded from a remote JournalNode
+   */
+  File getSyncLogTemporaryFile(long segmentTxId, long epoch) {
+    String name = NNStorage.getInProgressEditsFileName(segmentTxId) +
+        ".epoch=" + epoch; 
+    return new File(sd.getCurrentDir(), name);
+  }
+
+  /**
+   * @return the path for the file which contains persisted data for the
+   * paxos-like recovery process for the given log segment.
+   */
+  File getPaxosFile(long segmentTxId) {
+    return new File(getPaxosDir(), String.valueOf(segmentTxId));
+  }
+  
+  File getPaxosDir() {
+    return new File(sd.getCurrentDir(), "paxos");
+  }
+  
+  /**
+   * Remove any log files and associated paxos files which are older than
+   * the given txid.
+   */
+  void purgeDataOlderThan(long minTxIdToKeep) throws IOException {
+    purgeMatching(sd.getCurrentDir(),
+        CURRENT_DIR_PURGE_REGEXES, minTxIdToKeep);
+    purgeMatching(getPaxosDir(), PAXOS_DIR_PURGE_REGEXES, minTxIdToKeep);
+  }
+  
+  /**
+   * Purge files in the given directory which match any of the set of patterns.
+   * The patterns must have a single numeric capture group which determines
+   * the associated transaction ID of the file. Only those files for which
+   * the transaction ID is less than the <code>minTxIdToKeep</code> parameter
+   * are removed.
+   */
+  private static void purgeMatching(File dir, List<Pattern> patterns,
+      long minTxIdToKeep) throws IOException {
+
+    for (File f : FileUtil.listFiles(dir)) {
+      if (!f.isFile()) continue;
+      
+      for (Pattern p : patterns) {
+        Matcher matcher = p.matcher(f.getName());
+        if (matcher.matches()) {
+          // This parsing will always succeed since the group(1) is
+          // /\d+/ in the regex itself.
+          long txid = Long.valueOf(matcher.group(1));
+          if (txid < minTxIdToKeep) {
+            LOG.info("Purging no-longer needed file " + txid);
+            if (!f.delete()) {
+              LOG.warn("Unable to delete no-longer-needed data " +
+                  f);
+            }
+            break;
+          }
+        }
+      }
+    }
+  }
+
+  void format(NamespaceInfo nsInfo) throws IOException {
+    setStorageInfo(nsInfo);
+    LOG.info("Formatting journal storage directory " + 
+        sd + " with nsid: " + getNamespaceID());
+    // Unlock the directory before formatting, because we will
+    // re-analyze it after format(). The analyzeStorage() call
+    // below is reponsible for re-locking it. This is a no-op
+    // if the storage is not currently locked.
+    unlockAll();
+    sd.clearDirectory();
+    writeProperties(sd);
+    if (!getPaxosDir().mkdirs()) {
+      throw new IOException("Could not create paxos dir: " + getPaxosDir());
+    }
+    analyzeStorage();
+  }
+
+  
+  void analyzeStorage() throws IOException {
+    this.state = sd.analyzeStorage(StartupOption.REGULAR, this);
+    if (state == StorageState.NORMAL) {
+      readProperties(sd);
+    }
+  }
+
+  void checkConsistentNamespace(NamespaceInfo nsInfo)
+      throws IOException {
+    if (nsInfo.getNamespaceID() != getNamespaceID()) {
+      throw new IOException("Incompatible namespaceID for journal " +
+          this.sd + ": NameNode has nsId " + nsInfo.getNamespaceID() +
+          " but storage has nsId " + getNamespaceID());
+    }
+    
+    if (!nsInfo.getClusterID().equals(getClusterID())) {
+      throw new IOException("Incompatible clusterID for journal " +
+          this.sd + ": NameNode has clusterId '" + nsInfo.getClusterID() +
+          "' but storage has clusterId '" + getClusterID() + "'");
+      
+    }
+  }
+
+  public void close() throws IOException {
+    LOG.info("Closing journal storage for " + sd);
+    unlockAll();
+  }
+
+  public boolean isFormatted() {
+    return state == StorageState.NORMAL;
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/Journal.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/Journal.java
new file mode 100644
index 0000000..9a15fc1
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/Journal.java
@@ -0,0 +1,953 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import java.io.Closeable;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStreamWriter;
+import java.net.URL;
+import java.security.PrivilegedExceptionAction;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.fs.FileUtil;
+import org.apache.hadoop.hdfs.protocol.HdfsConstants;
+import org.apache.hadoop.hdfs.qjournal.protocol.JournalNotFormattedException;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
+import org.apache.hadoop.hdfs.qjournal.protocol.JournalOutOfSyncException;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PersistedRecoveryPaxosData;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
+import org.apache.hadoop.hdfs.server.common.StorageErrorReporter;
+import org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream;
+import org.apache.hadoop.hdfs.server.namenode.FileJournalManager;
+import org.apache.hadoop.hdfs.server.namenode.FileJournalManager.EditLogFile;
+import org.apache.hadoop.hdfs.server.namenode.JournalManager;
+import org.apache.hadoop.hdfs.server.namenode.TransferFsImage;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.server.protocol.RemoteEditLogManifest;
+import org.apache.hadoop.hdfs.util.AtomicFileOutputStream;
+import org.apache.hadoop.hdfs.util.BestEffortLongFile;
+import org.apache.hadoop.hdfs.util.PersistentLongFile;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.ipc.Server;
+import org.apache.hadoop.security.SecurityUtil;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import com.google.common.base.Stopwatch;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Range;
+import com.google.common.collect.Ranges;
+import com.google.protobuf.TextFormat;
+
+/**
+ * A JournalNode can manage journals for several clusters at once.
+ * Each such journal is entirely independent despite being hosted by
+ * the same JVM.
+ */
+class Journal implements Closeable {
+  static final Log LOG = LogFactory.getLog(Journal.class);
+
+
+  // Current writing state
+  private EditLogOutputStream curSegment;
+  private long curSegmentTxId = HdfsConstants.INVALID_TXID;
+  private long nextTxId = HdfsConstants.INVALID_TXID;
+  private long highestWrittenTxId = 0;
+  
+  private final String journalId;
+  
+  private final JNStorage storage;
+
+  /**
+   * When a new writer comes along, it asks each node to promise
+   * to ignore requests from any previous writer, as identified
+   * by epoch number. In order to make such a promise, the epoch
+   * number of that writer is stored persistently on disk.
+   */
+  private PersistentLongFile lastPromisedEpoch;
+
+  /**
+   * Each IPC that comes from a given client contains a serial number
+   * which only increases from the client's perspective. Whenever
+   * we switch epochs, we reset this back to -1. Whenever an IPC
+   * comes from a client, we ensure that it is strictly higher
+   * than any previous IPC. This guards against any bugs in the IPC
+   * layer that would re-order IPCs or cause a stale retry from an old
+   * request to resurface and confuse things.
+   */
+  private long currentEpochIpcSerial = -1;
+  
+  /**
+   * The epoch number of the last writer to actually write a transaction.
+   * This is used to differentiate log segments after a crash at the very
+   * beginning of a segment. See the the 'testNewerVersionOfSegmentWins'
+   * test case.
+   */
+  private PersistentLongFile lastWriterEpoch;
+  
+  /**
+   * Lower-bound on the last committed transaction ID. This is not
+   * depended upon for correctness, but acts as a sanity check
+   * during the recovery procedures, and as a visibility mark
+   * for clients reading in-progress logs.
+   */
+  private BestEffortLongFile committedTxnId;
+  
+  private static final String LAST_PROMISED_FILENAME = "last-promised-epoch";
+  private static final String LAST_WRITER_EPOCH = "last-writer-epoch";
+  private static final String COMMITTED_TXID_FILENAME = "committed-txid";
+  
+  private final FileJournalManager fjm;
+
+  private final JournalMetrics metrics;
+
+
+  Journal(File logDir, String journalId,
+      StorageErrorReporter errorReporter) throws IOException {
+    storage = new JNStorage(logDir, errorReporter);
+    this.journalId = journalId;
+
+    refreshCachedData();
+    
+    this.fjm = storage.getJournalManager();
+    
+    this.metrics = JournalMetrics.create(this);
+    
+    EditLogFile latest = scanStorageForLatestEdits();
+    if (latest != null) {
+      highestWrittenTxId = latest.getLastTxId();
+    }
+  }
+
+  /**
+   * Reload any data that may have been cached. This is necessary
+   * when we first load the Journal, but also after any formatting
+   * operation, since the cached data is no longer relevant.
+   */
+  private synchronized void refreshCachedData() {
+    IOUtils.closeStream(committedTxnId);
+    
+    File currentDir = storage.getSingularStorageDir().getCurrentDir();
+    this.lastPromisedEpoch = new PersistentLongFile(
+        new File(currentDir, LAST_PROMISED_FILENAME), 0);
+    this.lastWriterEpoch = new PersistentLongFile(
+        new File(currentDir, LAST_WRITER_EPOCH), 0);
+    this.committedTxnId = new BestEffortLongFile(
+        new File(currentDir, COMMITTED_TXID_FILENAME),
+        HdfsConstants.INVALID_TXID);
+  }
+  
+  /**
+   * Scan the local storage directory, and return the segment containing
+   * the highest transaction.
+   * @return the EditLogFile with the highest transactions, or null
+   * if no files exist.
+   */
+  private synchronized EditLogFile scanStorageForLatestEdits() throws IOException {
+    if (!fjm.getStorageDirectory().getCurrentDir().exists()) {
+      return null;
+    }
+    
+    LOG.info("Scanning storage " + fjm);
+    List<EditLogFile> files = fjm.getLogFiles(0);
+    
+    while (!files.isEmpty()) {
+      EditLogFile latestLog = files.remove(files.size() - 1);
+      latestLog.validateLog();
+      LOG.info("Latest log is " + latestLog);
+      if (latestLog.getLastTxId() == HdfsConstants.INVALID_TXID) {
+        // the log contains no transactions
+        LOG.warn("Latest log " + latestLog + " has no transactions. " +
+            "moving it aside and looking for previous log");
+        latestLog.moveAsideEmptyFile();
+      } else {
+        return latestLog;
+      }
+    }
+    
+    LOG.info("No files in " + fjm);
+    return null;
+  }
+
+  /**
+   * Format the local storage with the given namespace.
+   */
+  void format(NamespaceInfo nsInfo) throws IOException {
+    Preconditions.checkState(nsInfo.getNamespaceID() != 0,
+        "can't format with uninitialized namespace info: %s",
+        nsInfo);
+    LOG.info("Formatting " + this + " with namespace info: " +
+        nsInfo);
+    storage.format(nsInfo);
+    refreshCachedData();
+  }
+
+  /**
+   * Unlock and release resources.
+   */
+  @Override // Closeable
+  public void close() throws IOException {
+    storage.close();
+    
+    IOUtils.closeStream(committedTxnId);
+  }
+  
+  JNStorage getStorage() {
+    return storage;
+  }
+  
+  String getJournalId() {
+    return journalId;
+  }
+
+  /**
+   * @return the last epoch which this node has promised not to accept
+   * any lower epoch, or 0 if no promises have been made.
+   */
+  synchronized long getLastPromisedEpoch() throws IOException {
+    checkFormatted();
+    return lastPromisedEpoch.get();
+  }
+
+  synchronized public long getLastWriterEpoch() throws IOException {
+    checkFormatted();
+    return lastWriterEpoch.get();
+  }
+  
+  synchronized long getCommittedTxnIdForTests() throws IOException {
+    return committedTxnId.get();
+  }
+  
+  synchronized long getCurrentLagTxns() throws IOException {
+    long committed = committedTxnId.get();
+    if (committed == 0) {
+      return 0;
+    }
+    
+    return Math.max(committed - highestWrittenTxId, 0L);
+  }
+  
+  synchronized long getHighestWrittenTxId() {
+    return highestWrittenTxId;
+  }
+  
+  @VisibleForTesting
+  JournalMetrics getMetricsForTests() {
+    return metrics;
+  }
+
+  /**
+   * Try to create a new epoch for this journal.
+   * @param nsInfo the namespace, which is verified for consistency or used to
+   * format, if the Journal has not yet been written to.
+   * @param epoch the epoch to start
+   * @return the status information necessary to begin recovery
+   * @throws IOException if the node has already made a promise to another
+   * writer with a higher epoch number, if the namespace is inconsistent,
+   * or if a disk error occurs.
+   */
+  synchronized NewEpochResponseProto newEpoch(
+      NamespaceInfo nsInfo, long epoch) throws IOException {
+
+    checkFormatted();
+    storage.checkConsistentNamespace(nsInfo);
+
+    // Check that the new epoch being proposed is in fact newer than
+    // any other that we've promised. 
+    if (epoch <= getLastPromisedEpoch()) {
+      throw new IOException("Proposed epoch " + epoch + " <= last promise " +
+          getLastPromisedEpoch());
+    }
+    
+    updateLastPromisedEpoch(epoch);
+    abortCurSegment();
+    
+    NewEpochResponseProto.Builder builder =
+        NewEpochResponseProto.newBuilder();
+
+    EditLogFile latestFile = scanStorageForLatestEdits();
+
+    if (latestFile != null) {
+      builder.setLastSegmentTxId(latestFile.getFirstTxId());
+    }
+    
+    return builder.build();
+  }
+
+  private void updateLastPromisedEpoch(long newEpoch) throws IOException {
+    LOG.info("Updating lastPromisedEpoch from " + lastPromisedEpoch.get() +
+        " to " + newEpoch + " for client " + Server.getRemoteIp());
+    lastPromisedEpoch.set(newEpoch);
+    
+    // Since we have a new writer, reset the IPC serial - it will start
+    // counting again from 0 for this writer.
+    currentEpochIpcSerial = -1;
+  }
+
+  private void abortCurSegment() throws IOException {
+    if (curSegment == null) {
+      return;
+    }
+    
+    curSegment.abort();
+    curSegment = null;
+    curSegmentTxId = HdfsConstants.INVALID_TXID;
+  }
+
+  /**
+   * Write a batch of edits to the journal.
+   * {@see QJournalProtocol#journal(RequestInfo, long, long, int, byte[])}
+   */
+  synchronized void journal(RequestInfo reqInfo,
+      long segmentTxId, long firstTxnId,
+      int numTxns, byte[] records) throws IOException {
+    checkFormatted();
+    checkWriteRequest(reqInfo);
+
+    checkSync(curSegment != null,
+        "Can't write, no segment open");
+    
+    if (curSegmentTxId != segmentTxId) {
+      // Sanity check: it is possible that the writer will fail IPCs
+      // on both the finalize() and then the start() of the next segment.
+      // This could cause us to continue writing to an old segment
+      // instead of rolling to a new one, which breaks one of the
+      // invariants in the design. If it happens, abort the segment
+      // and throw an exception.
+      JournalOutOfSyncException e = new JournalOutOfSyncException(
+          "Writer out of sync: it thinks it is writing segment " + segmentTxId
+          + " but current segment is " + curSegmentTxId);
+      abortCurSegment();
+      throw e;
+    }
+      
+    checkSync(nextTxId == firstTxnId,
+        "Can't write txid " + firstTxnId + " expecting nextTxId=" + nextTxId);
+    
+    long lastTxnId = firstTxnId + numTxns - 1;
+    if (LOG.isTraceEnabled()) {
+      LOG.trace("Writing txid " + firstTxnId + "-" + lastTxnId);
+    }
+
+    // If the edit has already been marked as committed, we know
+    // it has been fsynced on a quorum of other nodes, and we are
+    // "catching up" with the rest. Hence we do not need to fsync.
+    boolean isLagging = lastTxnId <= committedTxnId.get();
+    boolean shouldFsync = !isLagging;
+    
+    curSegment.writeRaw(records, 0, records.length);
+    curSegment.setReadyToFlush();
+    Stopwatch sw = new Stopwatch();
+    sw.start();
+    curSegment.flush(shouldFsync);
+    sw.stop();
+    
+    metrics.addSync(sw.elapsedTime(TimeUnit.MICROSECONDS));
+
+    if (isLagging) {
+      // This batch of edits has already been committed on a quorum of other
+      // nodes. So, we are in "catch up" mode. This gets its own metric.
+      metrics.batchesWrittenWhileLagging.incr(1);
+    }
+    
+    metrics.batchesWritten.incr(1);
+    metrics.bytesWritten.incr(records.length);
+    metrics.txnsWritten.incr(numTxns);
+    
+    highestWrittenTxId = lastTxnId;
+    nextTxId = lastTxnId + 1;
+  }
+
+  public void heartbeat(RequestInfo reqInfo) throws IOException {
+    checkRequest(reqInfo);
+  }
+  
+  /**
+   * Ensure that the given request is coming from the correct writer and in-order.
+   * @param reqInfo the request info
+   * @throws IOException if the request is invalid.
+   */
+  private synchronized void checkRequest(RequestInfo reqInfo) throws IOException {
+    // Invariant 25 from ZAB paper
+    if (reqInfo.getEpoch() < lastPromisedEpoch.get()) {
+      throw new IOException("IPC's epoch " + reqInfo.getEpoch() +
+          " is less than the last promised epoch " +
+          lastPromisedEpoch.get());
+    } else if (reqInfo.getEpoch() > lastPromisedEpoch.get()) {
+      // A newer client has arrived. Fence any previous writers by updating
+      // the promise.
+      updateLastPromisedEpoch(reqInfo.getEpoch());
+    }
+    
+    // Ensure that the IPCs are arriving in-order as expected.
+    checkSync(reqInfo.getIpcSerialNumber() > currentEpochIpcSerial,
+        "IPC serial %s from client %s was not higher than prior highest " +
+        "IPC serial %s", reqInfo.getIpcSerialNumber(),
+        Server.getRemoteIp(),
+        currentEpochIpcSerial);
+    currentEpochIpcSerial = reqInfo.getIpcSerialNumber();
+
+    if (reqInfo.hasCommittedTxId()) {
+      Preconditions.checkArgument(
+          reqInfo.getCommittedTxId() >= committedTxnId.get(),
+          "Client trying to move committed txid backward from " +
+          committedTxnId.get() + " to " + reqInfo.getCommittedTxId());
+      
+      committedTxnId.set(reqInfo.getCommittedTxId());
+    }
+  }
+  
+  private synchronized void checkWriteRequest(RequestInfo reqInfo) throws IOException {
+    checkRequest(reqInfo);
+    
+    if (reqInfo.getEpoch() != lastWriterEpoch.get()) {
+      throw new IOException("IPC's epoch " + reqInfo.getEpoch() +
+          " is not the current writer epoch  " +
+          lastWriterEpoch.get());
+    }
+  }
+  
+  public synchronized boolean isFormatted() {
+    return storage.isFormatted();
+  }
+
+  private void checkFormatted() throws JournalNotFormattedException {
+    if (!isFormatted()) {
+      throw new JournalNotFormattedException("Journal " +
+          storage.getSingularStorageDir() + " not formatted");
+    }
+  }
+
+  /**
+   * @throws JournalOutOfSyncException if the given expression is not true.
+   * The message of the exception is formatted using the 'msg' and
+   * 'formatArgs' parameters.
+   */
+  private void checkSync(boolean expression, String msg,
+      Object... formatArgs) throws JournalOutOfSyncException {
+    if (!expression) {
+      throw new JournalOutOfSyncException(String.format(msg, formatArgs));
+    }
+  }
+
+  /**
+   * @throws AssertionError if the given expression is not true.
+   * The message of the exception is formatted using the 'msg' and
+   * 'formatArgs' parameters.
+   * 
+   * This should be used in preference to Java's built-in assert in
+   * non-performance-critical paths, where a failure of this invariant
+   * might cause the protocol to lose data. 
+   */
+  private void alwaysAssert(boolean expression, String msg,
+      Object... formatArgs) {
+    if (!expression) {
+      throw new AssertionError(String.format(msg, formatArgs));
+    }
+  }
+  
+  /**
+   * Start a new segment at the given txid. The previous segment
+   * must have already been finalized.
+   */
+  public synchronized void startLogSegment(RequestInfo reqInfo, long txid)
+      throws IOException {
+    assert fjm != null;
+    checkFormatted();
+    checkRequest(reqInfo);
+    
+    if (curSegment != null) {
+      LOG.warn("Client is requesting a new log segment " + txid + 
+          " though we are already writing " + curSegment + ". " +
+          "Aborting the current segment in order to begin the new one.");
+      // The writer may have lost a connection to us and is now
+      // re-connecting after the connection came back.
+      // We should abort our own old segment.
+      abortCurSegment();
+    }
+
+    // Paranoid sanity check: we should never overwrite a finalized log file.
+    // Additionally, if it's in-progress, it should have at most 1 transaction.
+    // This can happen if the writer crashes exactly at the start of a segment.
+    EditLogFile existing = fjm.getLogFile(txid);
+    if (existing != null) {
+      if (!existing.isInProgress()) {
+        throw new IllegalStateException("Already have a finalized segment " +
+            existing + " beginning at " + txid);
+      }
+      
+      // If it's in-progress, it should only contain one transaction,
+      // because the "startLogSegment" transaction is written alone at the
+      // start of each segment. 
+      existing.validateLog();
+      if (existing.getLastTxId() != existing.getFirstTxId()) {
+        throw new IllegalStateException("The log file " +
+            existing + " seems to contain valid transactions");
+      }
+    }
+    
+    long curLastWriterEpoch = lastWriterEpoch.get();
+    if (curLastWriterEpoch != reqInfo.getEpoch()) {
+      LOG.info("Updating lastWriterEpoch from " + curLastWriterEpoch +
+          " to " + reqInfo.getEpoch() + " for client " +
+          Server.getRemoteIp());
+      lastWriterEpoch.set(reqInfo.getEpoch());
+    }
+
+    // The fact that we are starting a segment at this txid indicates
+    // that any previous recovery for this same segment was aborted.
+    // Otherwise, no writer would have started writing. So, we can
+    // remove the record of the older segment here.
+    purgePaxosDecision(txid);
+    
+    curSegment = fjm.startLogSegment(txid);
+    curSegmentTxId = txid;
+    nextTxId = txid;
+  }
+  
+  /**
+   * Finalize the log segment at the given transaction ID.
+   */
+  public synchronized void finalizeLogSegment(RequestInfo reqInfo, long startTxId,
+      long endTxId) throws IOException {
+    checkFormatted();
+    checkRequest(reqInfo);
+
+    boolean needsValidation = true;
+
+    // Finalizing the log that the writer was just writing.
+    if (startTxId == curSegmentTxId) {
+      if (curSegment != null) {
+        curSegment.close();
+        curSegment = null;
+        curSegmentTxId = HdfsConstants.INVALID_TXID;
+      }
+      
+      checkSync(nextTxId == endTxId + 1,
+          "Trying to finalize in-progress log segment %s to end at " +
+          "txid %s but only written up to txid %s",
+          startTxId, endTxId, nextTxId - 1);
+      // No need to validate the edit log if the client is finalizing
+      // the log segment that it was just writing to.
+      needsValidation = false;
+    }
+    
+    FileJournalManager.EditLogFile elf = fjm.getLogFile(startTxId);
+    if (elf == null) {
+      throw new JournalOutOfSyncException("No log file to finalize at " +
+          "transaction ID " + startTxId);
+    }
+
+    if (elf.isInProgress()) {
+      if (needsValidation) {
+        LOG.info("Validating log segment " + elf.getFile() + " about to be " +
+            "finalized");
+        elf.validateLog();
+  
+        checkSync(elf.getLastTxId() == endTxId,
+            "Trying to finalize in-progress log segment %s to end at " +
+            "txid %s but log %s on disk only contains up to txid %s",
+            startTxId, endTxId, elf.getFile(), elf.getLastTxId());
+      }
+      fjm.finalizeLogSegment(startTxId, endTxId);
+    } else {
+      Preconditions.checkArgument(endTxId == elf.getLastTxId(),
+          "Trying to re-finalize already finalized log " +
+              elf + " with different endTxId " + endTxId);
+    }
+
+    // Once logs are finalized, a different length will never be decided.
+    // During recovery, we treat a finalized segment the same as an accepted
+    // recovery. Thus, we no longer need to keep track of the previously-
+    // accepted decision. The existence of the finalized log segment is enough.
+    purgePaxosDecision(elf.getFirstTxId());
+  }
+  
+  /**
+   * @see JournalManager#purgeLogsOlderThan(long)
+   */
+  public synchronized void purgeLogsOlderThan(RequestInfo reqInfo,
+      long minTxIdToKeep) throws IOException {
+    checkFormatted();
+    checkRequest(reqInfo);
+    
+    storage.purgeDataOlderThan(minTxIdToKeep);
+  }
+  
+  /**
+   * Remove the previously-recorded 'accepted recovery' information
+   * for a given log segment, once it is no longer necessary. 
+   * @param segmentTxId the transaction ID to purge
+   * @throws IOException if the file could not be deleted
+   */
+  private void purgePaxosDecision(long segmentTxId) throws IOException {
+    File paxosFile = storage.getPaxosFile(segmentTxId);
+    if (paxosFile.exists()) {
+      if (!paxosFile.delete()) {
+        throw new IOException("Unable to delete paxos file " + paxosFile);
+      }
+    }
+  }
+
+  /**
+   * @see QJournalProtocol#getEditLogManifest(String, long)
+   */
+  public RemoteEditLogManifest getEditLogManifest(long sinceTxId)
+      throws IOException {
+    // No need to checkRequest() here - anyone may ask for the list
+    // of segments.
+    checkFormatted();
+    
+    RemoteEditLogManifest manifest = new RemoteEditLogManifest(
+        fjm.getRemoteEditLogs(sinceTxId));
+    return manifest;
+  }
+
+  /**
+   * @return the current state of the given segment, or null if the
+   * segment does not exist.
+   */
+  private SegmentStateProto getSegmentInfo(long segmentTxId)
+      throws IOException {
+    EditLogFile elf = fjm.getLogFile(segmentTxId);
+    if (elf == null) {
+      return null;
+    }
+    if (elf.isInProgress()) {
+      elf.validateLog();
+    }
+    if (elf.getLastTxId() == HdfsConstants.INVALID_TXID) {
+      LOG.info("Edit log file " + elf + " appears to be empty. " +
+          "Moving it aside...");
+      elf.moveAsideEmptyFile();
+      return null;
+    }
+    SegmentStateProto ret = SegmentStateProto.newBuilder()
+        .setStartTxId(segmentTxId)
+        .setEndTxId(elf.getLastTxId())
+        .setIsInProgress(elf.isInProgress())
+        .build();
+    LOG.info("getSegmentInfo(" + segmentTxId + "): " + elf + " -> " +
+        TextFormat.shortDebugString(ret));
+    return ret;
+  }
+
+  /**
+   * @see QJournalProtocol#prepareRecovery(RequestInfo, long)
+   */
+  public synchronized PrepareRecoveryResponseProto prepareRecovery(
+      RequestInfo reqInfo, long segmentTxId) throws IOException {
+    checkFormatted();
+    checkRequest(reqInfo);
+    
+    abortCurSegment();
+    
+    PrepareRecoveryResponseProto.Builder builder =
+        PrepareRecoveryResponseProto.newBuilder();
+
+    PersistedRecoveryPaxosData previouslyAccepted = getPersistedPaxosData(segmentTxId);
+    completeHalfDoneAcceptRecovery(previouslyAccepted);
+
+    SegmentStateProto segInfo = getSegmentInfo(segmentTxId);
+    boolean hasFinalizedSegment = segInfo != null && !segInfo.getIsInProgress();
+
+    if (previouslyAccepted != null && !hasFinalizedSegment) {
+      SegmentStateProto acceptedState = previouslyAccepted.getSegmentState();
+      assert acceptedState.getEndTxId() == segInfo.getEndTxId() :
+            "prev accepted: " + TextFormat.shortDebugString(previouslyAccepted)+ "\n" +
+            "on disk:       " + TextFormat.shortDebugString(segInfo);
+            
+      builder.setAcceptedInEpoch(previouslyAccepted.getAcceptedInEpoch())
+        .setSegmentState(previouslyAccepted.getSegmentState());
+    } else {
+      if (segInfo != null) {
+        builder.setSegmentState(segInfo);
+      }
+    }
+    
+    builder.setLastWriterEpoch(lastWriterEpoch.get());
+    if (committedTxnId.get() != HdfsConstants.INVALID_TXID) {
+      builder.setLastCommittedTxId(committedTxnId.get());
+    }
+    
+    PrepareRecoveryResponseProto resp = builder.build();
+    LOG.info("Prepared recovery for segment " + segmentTxId + ": " +
+        TextFormat.shortDebugString(resp));
+    return resp;
+  }
+  
+  /**
+   * @see QJournalProtocol#acceptRecovery(RequestInfo, SegmentStateProto, URL)
+   */
+  public synchronized void acceptRecovery(RequestInfo reqInfo,
+      SegmentStateProto segment, URL fromUrl)
+      throws IOException {
+    checkFormatted();
+    checkRequest(reqInfo);
+    
+    abortCurSegment();
+
+    long segmentTxId = segment.getStartTxId();
+
+    // Basic sanity checks that the segment is well-formed and contains
+    // at least one transaction.
+    Preconditions.checkArgument(segment.getEndTxId() > 0 &&
+        segment.getEndTxId() >= segmentTxId,
+        "bad recovery state for segment %s: %s",
+        segmentTxId, TextFormat.shortDebugString(segment));
+    
+    PersistedRecoveryPaxosData oldData = getPersistedPaxosData(segmentTxId);
+    PersistedRecoveryPaxosData newData = PersistedRecoveryPaxosData.newBuilder()
+        .setAcceptedInEpoch(reqInfo.getEpoch())
+        .setSegmentState(segment)
+        .build();
+    
+    // If we previously acted on acceptRecovery() from a higher-numbered writer,
+    // this call is out of sync. We should never actually trigger this, since the
+    // checkRequest() call above should filter non-increasing epoch numbers.
+    if (oldData != null) {
+      alwaysAssert(oldData.getAcceptedInEpoch() <= reqInfo.getEpoch(),
+          "Bad paxos transition, out-of-order epochs.\nOld: %s\nNew: %s\n",
+          oldData, newData);
+    }
+    
+    File syncedFile = null;
+    
+    SegmentStateProto currentSegment = getSegmentInfo(segmentTxId);
+    if (currentSegment == null ||
+        currentSegment.getEndTxId() != segment.getEndTxId()) {
+      if (currentSegment == null) {
+        LOG.info("Synchronizing log " + TextFormat.shortDebugString(segment) +
+            ": no current segment in place");
+        
+        // Update the highest txid for lag metrics
+        highestWrittenTxId = Math.max(segment.getEndTxId(),
+            highestWrittenTxId);
+      } else {
+        LOG.info("Synchronizing log " + TextFormat.shortDebugString(segment) +
+            ": old segment " + TextFormat.shortDebugString(currentSegment) +
+            " is not the right length");
+        
+        // Paranoid sanity check: if the new log is shorter than the log we
+        // currently have, we should not end up discarding any transactions
+        // which are already Committed.
+        if (txnRange(currentSegment).contains(committedTxnId.get()) &&
+            !txnRange(segment).contains(committedTxnId.get())) {
+          throw new AssertionError(
+              "Cannot replace segment " +
+              TextFormat.shortDebugString(currentSegment) +
+              " with new segment " +
+              TextFormat.shortDebugString(segment) + 
+              ": would discard already-committed txn " +
+              committedTxnId.get());
+        }
+        
+        // Another paranoid check: we should not be asked to synchronize a log
+        // on top of a finalized segment.
+        alwaysAssert(currentSegment.getIsInProgress(),
+            "Should never be asked to synchronize a different log on top of an " +
+            "already-finalized segment");
+        
+        // If we're shortening the log, update our highest txid
+        // used for lag metrics.
+        if (txnRange(currentSegment).contains(highestWrittenTxId)) {
+          highestWrittenTxId = segment.getEndTxId();
+        }
+      }
+      syncedFile = syncLog(reqInfo, segment, fromUrl);
+      
+    } else {
+      LOG.info("Skipping download of log " +
+          TextFormat.shortDebugString(segment) +
+          ": already have up-to-date logs");
+    }
+    
+    // This is one of the few places in the protocol where we have a single
+    // RPC that results in two distinct actions:
+    //
+    // - 1) Downloads the new log segment data (above)
+    // - 2) Records the new Paxos data about the synchronized segment (below)
+    //
+    // These need to be treated as a transaction from the perspective
+    // of any external process. We do this by treating the persistPaxosData()
+    // success as the "commit" of an atomic transaction. If we fail before
+    // this point, the downloaded edit log will only exist at a temporary
+    // path, and thus not change any externally visible state. If we fail
+    // after this point, then any future prepareRecovery() call will see
+    // the Paxos data, and by calling completeHalfDoneAcceptRecovery() will
+    // roll forward the rename of the referenced log file.
+    //
+    // See also: HDFS-3955
+    //
+    // The fault points here are exercised by the randomized fault injection
+    // test case to ensure that this atomic "transaction" operates correctly.
+    JournalFaultInjector.get().beforePersistPaxosData();
+    persistPaxosData(segmentTxId, newData);
+    JournalFaultInjector.get().afterPersistPaxosData();
+
+    if (syncedFile != null) {
+      FileUtil.replaceFile(syncedFile,
+          storage.getInProgressEditLog(segmentTxId));
+    }
+
+    LOG.info("Accepted recovery for segment " + segmentTxId + ": " +
+        TextFormat.shortDebugString(newData));
+  }
+
+  private Range<Long> txnRange(SegmentStateProto seg) {
+    Preconditions.checkArgument(seg.hasEndTxId(),
+        "invalid segment: %s", seg);
+    return Ranges.closed(seg.getStartTxId(), seg.getEndTxId());
+  }
+
+  /**
+   * Synchronize a log segment from another JournalNode. The log is
+   * downloaded from the provided URL into a temporary location on disk,
+   * which is named based on the current request's epoch.
+   *
+   * @return the temporary location of the downloaded file
+   */
+  private File syncLog(RequestInfo reqInfo,
+      final SegmentStateProto segment, final URL url) throws IOException {
+    final File tmpFile = storage.getSyncLogTemporaryFile(
+        segment.getStartTxId(), reqInfo.getEpoch());
+    final List<File> localPaths = ImmutableList.of(tmpFile);
+
+    LOG.info("Synchronizing log " +
+        TextFormat.shortDebugString(segment) + " from " + url);
+    SecurityUtil.doAsLoginUser(
+        new PrivilegedExceptionAction<Void>() {
+          @Override
+          public Void run() throws IOException {
+            boolean success = false;
+            try {
+              TransferFsImage.doGetUrl(url, localPaths, storage, true);
+              assert tmpFile.exists();
+              success = true;
+            } finally {
+              if (!success) {
+                if (!tmpFile.delete()) {
+                  LOG.warn("Failed to delete temporary file " + tmpFile);
+                }
+              }
+            }
+            return null;
+          }
+        });
+    return tmpFile;
+  }
+  
+
+  /**
+   * In the case the node crashes in between downloading a log segment
+   * and persisting the associated paxos recovery data, the log segment
+   * will be left in its temporary location on disk. Given the paxos data,
+   * we can check if this was indeed the case, and &quot;roll forward&quot;
+   * the atomic operation.
+   * 
+   * See the inline comments in
+   * {@link #acceptRecovery(RequestInfo, SegmentStateProto, URL)} for more
+   * details.
+   *
+   * @throws IOException if the temporary file is unable to be renamed into
+   * place
+   */
+  private void completeHalfDoneAcceptRecovery(
+      PersistedRecoveryPaxosData paxosData) throws IOException {
+    if (paxosData == null) {
+      return;
+    }
+
+    long segmentId = paxosData.getSegmentState().getStartTxId();
+    long epoch = paxosData.getAcceptedInEpoch();
+    
+    File tmp = storage.getSyncLogTemporaryFile(segmentId, epoch);
+    
+    if (tmp.exists()) {
+      File dst = storage.getInProgressEditLog(segmentId);
+      LOG.info("Rolling forward previously half-completed synchronization: " +
+          tmp + " -> " + dst);
+      FileUtil.replaceFile(tmp, dst);
+    }
+  }
+
+  /**
+   * Retrieve the persisted data for recovering the given segment from disk.
+   */
+  private PersistedRecoveryPaxosData getPersistedPaxosData(long segmentTxId)
+      throws IOException {
+    File f = storage.getPaxosFile(segmentTxId);
+    if (!f.exists()) {
+      // Default instance has no fields filled in (they're optional)
+      return null;
+    }
+    
+    InputStream in = new FileInputStream(f);
+    try {
+      PersistedRecoveryPaxosData ret = PersistedRecoveryPaxosData.parseDelimitedFrom(in);
+      Preconditions.checkState(ret != null &&
+          ret.getSegmentState().getStartTxId() == segmentTxId,
+          "Bad persisted data for segment %s: %s",
+          segmentTxId, ret);
+      return ret;
+    } finally {
+      IOUtils.closeStream(in);
+    }
+  }
+
+  /**
+   * Persist data for recovering the given segment from disk.
+   */
+  private void persistPaxosData(long segmentTxId,
+      PersistedRecoveryPaxosData newData) throws IOException {
+    File f = storage.getPaxosFile(segmentTxId);
+    boolean success = false;
+    AtomicFileOutputStream fos = new AtomicFileOutputStream(f);
+    try {
+      newData.writeDelimitedTo(fos);
+      fos.write('\n');
+      // Write human-readable data after the protobuf. This is only
+      // to assist in debugging -- it's not parsed at all.
+      OutputStreamWriter writer = new OutputStreamWriter(fos);
+      
+      writer.write(String.valueOf(newData));
+      writer.write('\n');
+      writer.flush();
+      
+      fos.flush();
+      success = true;
+    } finally {
+      if (success) {
+        IOUtils.closeStream(fos);
+      } else {
+        fos.abort();
+      }
+    }
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalFaultInjector.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalFaultInjector.java
new file mode 100644
index 0000000..cefb7b5
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalFaultInjector.java
@@ -0,0 +1,41 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import java.io.IOException;
+
+import com.google.common.annotations.VisibleForTesting;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+/**
+ * Used for injecting faults in QuorumJournalManager tests.
+ * Calls into this are a no-op in production code. 
+ */
+@VisibleForTesting
+@InterfaceAudience.Private
+public class JournalFaultInjector {
+  public static JournalFaultInjector instance = new JournalFaultInjector();
+
+  public static JournalFaultInjector get() {
+    return instance;
+  }
+
+  public void beforePersistPaxosData() throws IOException {}
+  public void afterPersistPaxosData() throws IOException {}
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalMetrics.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalMetrics.java
new file mode 100644
index 0000000..7bbee5b
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalMetrics.java
@@ -0,0 +1,118 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import java.io.IOException;
+
+import org.apache.hadoop.metrics2.annotation.Metric;
+import org.apache.hadoop.metrics2.annotation.Metrics;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
+import org.apache.hadoop.metrics2.lib.MetricsRegistry;
+import org.apache.hadoop.metrics2.lib.MutableCounterLong;
+import org.apache.hadoop.metrics2.lib.MutableQuantiles;
+
+/**
+ * The server-side metrics for a journal from the JournalNode's
+ * perspective.
+ */
+@Metrics(about="Journal metrics", context="dfs")
+class JournalMetrics {
+  final MetricsRegistry registry = new MetricsRegistry("JournalNode");
+  
+  @Metric("Number of batches written since startup")
+  MutableCounterLong batchesWritten;
+  
+  @Metric("Number of txns written since startup")
+  MutableCounterLong txnsWritten;
+  
+  @Metric("Number of bytes written since startup")
+  MutableCounterLong bytesWritten;
+  
+  @Metric("Number of batches written where this node was lagging")
+  MutableCounterLong batchesWrittenWhileLagging;
+  
+  private final int[] QUANTILE_INTERVALS = new int[] {
+      1*60, // 1m
+      5*60, // 5m
+      60*60 // 1h
+  };
+  
+  MutableQuantiles[] syncsQuantiles;
+  
+  private final Journal journal;
+
+  JournalMetrics(Journal journal) {
+    this.journal = journal;
+    
+    syncsQuantiles = new MutableQuantiles[QUANTILE_INTERVALS.length];
+    for (int i = 0; i < syncsQuantiles.length; i++) {
+      int interval = QUANTILE_INTERVALS[i];
+      syncsQuantiles[i] = registry.newQuantiles(
+          "syncs" + interval + "s",
+          "Journal sync time", "ops", "latencyMicros", interval);
+    }
+  }
+  
+  public static JournalMetrics create(Journal j) {
+    JournalMetrics m = new JournalMetrics(j);
+    return DefaultMetricsSystem.instance().register(
+        m.getName(), null, m);
+  }
+
+  String getName() {
+    return "Journal-" + journal.getJournalId();
+  }
+
+  @Metric("Current writer's epoch")
+  public long getLastWriterEpoch() {
+    try {
+      return journal.getLastWriterEpoch();
+    } catch (IOException e) {
+      return -1L;
+    }
+  }
+  
+  @Metric("Last accepted epoch")
+  public long getLastPromisedEpoch() {
+    try {
+      return journal.getLastPromisedEpoch();
+    } catch (IOException e) {
+      return -1L;
+    }
+  }
+  
+  @Metric("The highest txid stored on this JN")
+  public long getLastWrittenTxId() {
+    return journal.getHighestWrittenTxId();
+  }
+  
+  @Metric("Number of transactions that this JN is lagging")
+  public long getCurrentLagTxns() {
+    try {
+      return journal.getCurrentLagTxns();
+    } catch (IOException e) {
+      return -1L;
+    }
+  }
+  
+  void addSync(long us) {
+    for (MutableQuantiles q : syncsQuantiles) {
+      q.add(us);
+    }
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNode.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNode.java
new file mode 100644
index 0000000..e70f469
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNode.java
@@ -0,0 +1,235 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.util.Map;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configurable;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager;
+import org.apache.hadoop.hdfs.server.common.StorageErrorReporter;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
+import org.apache.hadoop.metrics2.source.JvmMetrics;
+import org.apache.hadoop.security.SecurityUtil;
+import org.apache.hadoop.util.Tool;
+import org.apache.hadoop.util.ToolRunner;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Maps;
+
+/**
+ * The JournalNode is a daemon which allows namenodes using
+ * the QuorumJournalManager to log and retrieve edits stored
+ * remotely. It is a thin wrapper around a local edit log
+ * directory with the addition of facilities to participate
+ * in the quorum protocol.
+ */
+@InterfaceAudience.Private
+public class JournalNode implements Tool, Configurable {
+  public static final Log LOG = LogFactory.getLog(JournalNode.class);
+  private Configuration conf;
+  private JournalNodeRpcServer rpcServer;
+  private JournalNodeHttpServer httpServer;
+  private Map<String, Journal> journalsById = Maps.newHashMap();
+
+  private File localDir;
+
+  static {
+    HdfsConfiguration.init();
+  }
+  
+  /**
+   * When stopped, the daemon will exit with this code. 
+   */
+  private int resultCode = 0;
+
+  synchronized Journal getOrCreateJournal(String jid) throws IOException {
+    QuorumJournalManager.checkJournalId(jid);
+    
+    Journal journal = journalsById.get(jid);
+    if (journal == null) {
+      File logDir = getLogDir(jid);
+      LOG.info("Initializing journal in directory " + logDir);      
+      journal = new Journal(logDir, jid, new ErrorReporter());
+      journalsById.put(jid, journal);
+    }
+    
+    return journal;
+  }
+
+
+  @Override
+  public void setConf(Configuration conf) {
+    this.conf = conf;
+    this.localDir = new File(
+        conf.get(DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_KEY,
+        DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_DEFAULT).trim());
+  }
+
+  private static void validateAndCreateJournalDir(File dir) throws IOException {
+    if (!dir.isAbsolute()) {
+      throw new IllegalArgumentException(
+          "Journal dir '" + dir + "' should be an absolute path");
+    }
+
+    if (!dir.exists() && !dir.mkdirs()) {
+      throw new IOException("Could not create journal dir '" +
+          dir + "'");
+    } else if (!dir.isDirectory()) {
+      throw new IOException("Journal directory '" + dir + "' is not " +
+          "a directory");
+    }
+    
+    if (!dir.canWrite()) {
+      throw new IOException("Unable to write to journal dir '" +
+          dir + "'");
+    }
+  }
+
+
+  @Override
+  public Configuration getConf() {
+    return conf;
+  }
+
+  @Override
+  public int run(String[] args) throws Exception {
+    start();
+    return join();
+  }
+
+  /**
+   * Start listening for edits via RPC.
+   */
+  public void start() throws IOException {
+    Preconditions.checkState(!isStarted(), "JN already running");
+    
+    validateAndCreateJournalDir(localDir);
+    
+    DefaultMetricsSystem.initialize("JournalNode");
+    JvmMetrics.create("JournalNode",
+        conf.get(DFSConfigKeys.DFS_METRICS_SESSION_ID_KEY),
+        DefaultMetricsSystem.instance());
+
+    InetSocketAddress socAddr = JournalNodeRpcServer.getAddress(conf);
+    SecurityUtil.login(conf, DFSConfigKeys.DFS_JOURNALNODE_KEYTAB_FILE_KEY,
+        DFSConfigKeys.DFS_JOURNALNODE_USER_NAME_KEY, socAddr.getHostName());
+    
+    httpServer = new JournalNodeHttpServer(conf, this);
+    httpServer.start();
+
+    rpcServer = new JournalNodeRpcServer(conf, this);
+    rpcServer.start();
+  }
+
+  public boolean isStarted() {
+    return rpcServer != null;
+  }
+
+  /**
+   * @return the address the IPC server is bound to
+   */
+  public InetSocketAddress getBoundIpcAddress() {
+    return rpcServer.getAddress();
+  }
+  
+
+  public InetSocketAddress getBoundHttpAddress() {
+    return httpServer.getAddress();
+  }
+
+
+  /**
+   * Stop the daemon with the given status code
+   * @param rc the status code with which to exit (non-zero
+   * should indicate an error)
+   */
+  public void stop(int rc) {
+    this.resultCode = rc;
+    
+    if (rpcServer != null) { 
+      rpcServer.stop();
+    }
+
+    if (httpServer != null) {
+      try {
+        httpServer.stop();
+      } catch (IOException ioe) {
+        LOG.warn("Unable to stop HTTP server for " + this, ioe);
+      }
+    }
+    
+    for (Journal j : journalsById.values()) {
+      IOUtils.cleanup(LOG, j);
+    }
+  }
+
+  /**
+   * Wait for the daemon to exit.
+   * @return the result code (non-zero if error)
+   */
+  int join() throws InterruptedException {
+    if (rpcServer != null) {
+      rpcServer.join();
+    }
+    return resultCode;
+  }
+  
+  public void stopAndJoin(int rc) throws InterruptedException {
+    stop(rc);
+    join();
+  }
+
+  /**
+   * Return the directory inside our configured storage
+   * dir which corresponds to a given journal. 
+   * @param jid the journal identifier
+   * @return the file, which may or may not exist yet
+   */
+  private File getLogDir(String jid) {
+    String dir = conf.get(DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_KEY,
+        DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_DEFAULT);
+    Preconditions.checkArgument(jid != null &&
+        !jid.isEmpty(),
+        "bad journal identifier: %s", jid);
+    return new File(new File(dir), jid);
+  }
+
+  
+  private class ErrorReporter implements StorageErrorReporter {
+    @Override
+    public void reportErrorOnFile(File f) {
+      LOG.fatal("Error reported on file " + f + "... exiting",
+          new Exception());
+      stop(1);
+    }
+  }
+
+  public static void main(String[] args) throws Exception {
+    System.exit(ToolRunner.run(new JournalNode(), args));
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNodeHttpServer.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNodeHttpServer.java
new file mode 100644
index 0000000..7ad6f8d
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNodeHttpServer.java
@@ -0,0 +1,129 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_ADMIN;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_JOURNALNODE_KEYTAB_FILE_KEY;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_JOURNALNODE_INTERNAL_SPNEGO_USER_NAME_KEY;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+
+import javax.servlet.ServletContext;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.server.common.JspHelper;
+import org.apache.hadoop.http.HttpServer;
+import org.apache.hadoop.net.NetUtils;
+import org.apache.hadoop.security.authorize.AccessControlList;
+import org.apache.hadoop.security.UserGroupInformation;
+import org.apache.hadoop.security.SecurityUtil;
+
+/**
+ * Encapsulates the HTTP server started by the Journal Service.
+ */
+@InterfaceAudience.Private
+public class JournalNodeHttpServer {
+  public static final Log LOG = LogFactory.getLog(
+      JournalNodeHttpServer.class);
+
+  public static final String JN_ATTRIBUTE_KEY = "localjournal";
+
+  private HttpServer httpServer;
+  private int infoPort;
+  private JournalNode localJournalNode;
+
+  private final Configuration conf;
+
+  JournalNodeHttpServer(Configuration conf, JournalNode jn) {
+    this.conf = conf;
+    this.localJournalNode = jn;
+  }
+
+  void start() throws IOException {
+    final InetSocketAddress bindAddr = getAddress(conf);
+
+    // initialize the webserver for uploading/downloading files.
+    LOG.info("Starting web server as: "+ SecurityUtil.getServerPrincipal(conf
+        .get(DFS_JOURNALNODE_INTERNAL_SPNEGO_USER_NAME_KEY),
+        bindAddr.getHostName()));
+
+    int tmpInfoPort = bindAddr.getPort();
+    httpServer = new HttpServer("journal", bindAddr.getHostName(),
+        tmpInfoPort, tmpInfoPort == 0, conf, new AccessControlList(conf
+            .get(DFS_ADMIN, " "))) {
+      {
+        if (UserGroupInformation.isSecurityEnabled()) {
+          initSpnego(conf, DFS_JOURNALNODE_INTERNAL_SPNEGO_USER_NAME_KEY,
+              DFS_JOURNALNODE_KEYTAB_FILE_KEY);
+        }
+      }
+    };
+    httpServer.setAttribute(JN_ATTRIBUTE_KEY, localJournalNode);
+    httpServer.setAttribute(JspHelper.CURRENT_CONF, conf);
+    httpServer.addInternalServlet("getJournal", "/getJournal",
+        GetJournalEditServlet.class, true);
+    httpServer.start();
+
+    // The web-server port can be ephemeral... ensure we have the correct info
+    infoPort = httpServer.getPort();
+
+    LOG.info("Journal Web-server up at: " + bindAddr + ":" + infoPort);
+  }
+
+  void stop() throws IOException {
+    if (httpServer != null) {
+      try {
+        httpServer.stop();
+      } catch (Exception e) {
+        throw new IOException(e);
+      }
+    }
+  }
+  
+  /**
+   * Return the actual address bound to by the running server.
+   */
+  public InetSocketAddress getAddress() {
+    InetSocketAddress addr = httpServer.getListenerAddress();
+    assert addr.getPort() != 0;
+    return addr;
+  }
+
+  private static InetSocketAddress getAddress(Configuration conf) {
+    String addr = conf.get(DFSConfigKeys.DFS_JOURNALNODE_HTTP_ADDRESS_KEY,
+        DFSConfigKeys.DFS_JOURNALNODE_HTTP_ADDRESS_DEFAULT);
+    return NetUtils.createSocketAddr(addr,
+        DFSConfigKeys.DFS_JOURNALNODE_HTTP_PORT_DEFAULT,
+        DFSConfigKeys.DFS_JOURNALNODE_HTTP_ADDRESS_KEY);
+  }
+
+  public static Journal getJournalFromContext(ServletContext context, String jid)
+      throws IOException {
+    JournalNode jn = (JournalNode)context.getAttribute(JN_ATTRIBUTE_KEY);
+    return jn.getOrCreateJournal(jid);
+  }
+
+  public static Configuration getConfFromContext(ServletContext context) {
+    return (Configuration) context.getAttribute(JspHelper.CURRENT_CONF);
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNodeRpcServer.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNodeRpcServer.java
new file mode 100644
index 0000000..05a4956
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournalNodeRpcServer.java
@@ -0,0 +1,203 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.URL;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.HDFSPolicyProvider;
+import org.apache.hadoop.hdfs.protocolPB.PBHelper;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetEditLogManifestResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.QJournalProtocolService;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
+import org.apache.hadoop.hdfs.qjournal.protocolPB.QJournalProtocolPB;
+import org.apache.hadoop.hdfs.qjournal.protocolPB.QJournalProtocolServerSideTranslatorPB;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.server.protocol.RemoteEditLogManifest;
+import org.apache.hadoop.ipc.ProtobufRpcEngine;
+import org.apache.hadoop.ipc.RPC;
+import org.apache.hadoop.ipc.RPC.Server;
+import org.apache.hadoop.net.NetUtils;
+
+import com.google.protobuf.BlockingService;
+
+class JournalNodeRpcServer implements QJournalProtocol {
+
+  private static final int HANDLER_COUNT = 5;
+  private JournalNode jn;
+  private Server server;
+
+  JournalNodeRpcServer(Configuration conf, JournalNode jn) throws IOException {
+    this.jn = jn;
+    
+    Configuration confCopy = new Configuration(conf);
+    
+    // Ensure that nagling doesn't kick in, which could cause latency issues.
+    confCopy.setBoolean(
+        CommonConfigurationKeysPublic.IPC_SERVER_TCPNODELAY_KEY,
+        true);
+    
+    InetSocketAddress addr = getAddress(confCopy);
+    RPC.setProtocolEngine(confCopy, QJournalProtocolPB.class,
+        ProtobufRpcEngine.class);
+    QJournalProtocolServerSideTranslatorPB translator =
+        new QJournalProtocolServerSideTranslatorPB(this);
+    BlockingService service = QJournalProtocolService
+        .newReflectiveBlockingService(translator);
+    
+    this.server = new RPC.Builder(confCopy)
+      .setProtocol(QJournalProtocolPB.class)
+      .setInstance(service)
+      .setBindAddress(addr.getHostName())
+      .setPort(addr.getPort())
+      .setNumHandlers(HANDLER_COUNT)
+      .setVerbose(false)
+      .build();
+
+    // set service-level authorization security policy
+    if (confCopy.getBoolean(
+      CommonConfigurationKeys.HADOOP_SECURITY_AUTHORIZATION, false)) {
+          server.refreshServiceAcl(confCopy, new HDFSPolicyProvider());
+    }
+  }
+
+  void start() {
+    this.server.start();
+  }
+
+  public InetSocketAddress getAddress() {
+    return server.getListenerAddress();
+  }
+  
+  void join() throws InterruptedException {
+    this.server.join();
+  }
+  
+  void stop() {
+    this.server.stop();
+  }
+  
+  static InetSocketAddress getAddress(Configuration conf) {
+    String addr = conf.get(
+        DFSConfigKeys.DFS_JOURNALNODE_RPC_ADDRESS_KEY,
+        DFSConfigKeys.DFS_JOURNALNODE_RPC_ADDRESS_DEFAULT);
+    return NetUtils.createSocketAddr(addr, 0,
+        DFSConfigKeys.DFS_JOURNALNODE_RPC_ADDRESS_KEY);
+  }
+
+  @Override
+  public boolean isFormatted(String journalId) throws IOException {
+    return jn.getOrCreateJournal(journalId).isFormatted();
+  }
+
+  @Override
+  public GetJournalStateResponseProto getJournalState(String journalId)
+        throws IOException {
+    long epoch = jn.getOrCreateJournal(journalId).getLastPromisedEpoch(); 
+    return GetJournalStateResponseProto.newBuilder()
+        .setLastPromisedEpoch(epoch)
+        .setHttpPort(jn.getBoundHttpAddress().getPort())
+        .build();
+  }
+
+  @Override
+  public NewEpochResponseProto newEpoch(String journalId,
+      NamespaceInfo nsInfo,
+      long epoch) throws IOException {
+    return jn.getOrCreateJournal(journalId).newEpoch(nsInfo, epoch);
+  }
+
+  @Override
+  public void format(String journalId, NamespaceInfo nsInfo)
+      throws IOException {
+    jn.getOrCreateJournal(journalId).format(nsInfo);
+  }
+
+  @Override
+  public void journal(RequestInfo reqInfo,
+      long segmentTxId, long firstTxnId,
+      int numTxns, byte[] records) throws IOException {
+    jn.getOrCreateJournal(reqInfo.getJournalId())
+       .journal(reqInfo, segmentTxId, firstTxnId, numTxns, records);
+  }
+  
+  @Override
+  public void heartbeat(RequestInfo reqInfo) throws IOException {
+    jn.getOrCreateJournal(reqInfo.getJournalId())
+      .heartbeat(reqInfo);
+  }
+
+  @Override
+  public void startLogSegment(RequestInfo reqInfo, long txid)
+      throws IOException {
+    jn.getOrCreateJournal(reqInfo.getJournalId())
+      .startLogSegment(reqInfo, txid);
+  }
+
+  @Override
+  public void finalizeLogSegment(RequestInfo reqInfo, long startTxId,
+      long endTxId) throws IOException {
+    jn.getOrCreateJournal(reqInfo.getJournalId())
+      .finalizeLogSegment(reqInfo, startTxId, endTxId);
+  }
+
+  @Override
+  public void purgeLogsOlderThan(RequestInfo reqInfo, long minTxIdToKeep)
+      throws IOException {
+    jn.getOrCreateJournal(reqInfo.getJournalId())
+      .purgeLogsOlderThan(reqInfo, minTxIdToKeep);
+  }
+
+  @Override
+  public GetEditLogManifestResponseProto getEditLogManifest(String jid,
+      long sinceTxId) throws IOException {
+    
+    RemoteEditLogManifest manifest = jn.getOrCreateJournal(jid)
+        .getEditLogManifest(sinceTxId);
+    
+    return GetEditLogManifestResponseProto.newBuilder()
+        .setManifest(PBHelper.convert(manifest))
+        .setHttpPort(jn.getBoundHttpAddress().getPort())
+        .build();
+  }
+
+  @Override
+  public PrepareRecoveryResponseProto prepareRecovery(RequestInfo reqInfo,
+      long segmentTxId) throws IOException {
+    return jn.getOrCreateJournal(reqInfo.getJournalId())
+        .prepareRecovery(reqInfo, segmentTxId);
+  }
+
+  @Override
+  public void acceptRecovery(RequestInfo reqInfo, SegmentStateProto log,
+      URL fromUrl) throws IOException {
+    jn.getOrCreateJournal(reqInfo.getJournalId())
+        .acceptRecovery(reqInfo, log, fromUrl);
+  }
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/HdfsServerConstants.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/HdfsServerConstants.java
index c914035..50f6e73 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/HdfsServerConstants.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/HdfsServerConstants.java
@@ -39,7 +39,8 @@
    */
   static public enum NodeType {
     NAME_NODE,
-    DATA_NODE;
+    DATA_NODE,
+    JOURNAL_NODE;
   }
 
   /** Startup options */
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/Storage.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/Storage.java
index f89fbde..623d549 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/Storage.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/Storage.java
@@ -42,6 +42,8 @@
 import org.apache.hadoop.util.ToolRunner;
 import org.apache.hadoop.util.VersionInfo;
 
+import com.google.common.base.Preconditions;
+
 
 
 /**
@@ -76,7 +78,7 @@
   /** Layout versions of 0.20.203 release */
   public static final int[] LAYOUT_VERSIONS_203 = {-19, -31};
 
-  private   static final String STORAGE_FILE_LOCK     = "in_use.lock";
+  public    static final String STORAGE_FILE_LOCK     = "in_use.lock";
   protected static final String STORAGE_FILE_VERSION  = "VERSION";
   public    static final String STORAGE_DIR_CURRENT   = "current";
   public    static final String STORAGE_DIR_PREVIOUS  = "previous";
@@ -752,6 +754,15 @@
     return storageDirs.get(idx);
   }
   
+  /**
+   * @return the storage directory, with the precondition that this storage
+   * has exactly one storage directory
+   */
+  public StorageDirectory getSingularStorageDir() {
+    Preconditions.checkState(storageDirs.size() == 1);
+    return storageDirs.get(0);
+  }
+  
   protected void addStorageDir(StorageDirectory sd) {
     storageDirs.add(sd);
   }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogBackupOutputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogBackupOutputStream.java
index 5a28f7c..97cfe13 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogBackupOutputStream.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogBackupOutputStream.java
@@ -114,7 +114,7 @@
   }
 
   @Override // EditLogOutputStream
-  protected void flushAndSync() throws IOException {
+  protected void flushAndSync(boolean durable) throws IOException {
     assert out.getLength() == 0 : "Output buffer is not empty";
     
     int numReadyTxns = doubleBuf.countReadyTxns();
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogFileInputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogFileInputStream.java
index 1960415..76b5ff5 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogFileInputStream.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogFileInputStream.java
@@ -27,6 +27,7 @@
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.URL;
+import java.security.PrivilegedExceptionAction;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -367,30 +368,36 @@
 
     @Override
     public InputStream getInputStream() throws IOException {
-      HttpURLConnection connection = (HttpURLConnection)
-          SecurityUtil.openSecureHttpConnection(url);
-      
-      if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
-        throw new HttpGetFailedException(
-            "Fetch of " + url +
-            " failed with status code " + connection.getResponseCode() +
-            "\nResponse message:\n" + connection.getResponseMessage(),
-            connection);
-      }
-
-      String contentLength = connection.getHeaderField(CONTENT_LENGTH);
-      if (contentLength != null) {
-        advertisedSize = Long.parseLong(contentLength);
-        if (advertisedSize <= 0) {
-          throw new IOException("Invalid " + CONTENT_LENGTH + " header: " +
-              contentLength);
-        }
-      } else {
-        throw new IOException(CONTENT_LENGTH + " header is not provided " +
-                              "by the server when trying to fetch " + url);
-      }
-
-      return connection.getInputStream();
+      return SecurityUtil.doAsCurrentUser(
+          new PrivilegedExceptionAction<InputStream>() {
+            @Override
+            public InputStream run() throws IOException {
+              HttpURLConnection connection = (HttpURLConnection)
+                  SecurityUtil.openSecureHttpConnection(url);
+              
+              if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
+                throw new HttpGetFailedException(
+                    "Fetch of " + url +
+                    " failed with status code " + connection.getResponseCode() +
+                    "\nResponse message:\n" + connection.getResponseMessage(),
+                    connection);
+              }
+        
+              String contentLength = connection.getHeaderField(CONTENT_LENGTH);
+              if (contentLength != null) {
+                advertisedSize = Long.parseLong(contentLength);
+                if (advertisedSize <= 0) {
+                  throw new IOException("Invalid " + CONTENT_LENGTH + " header: " +
+                      contentLength);
+                }
+              } else {
+                throw new IOException(CONTENT_LENGTH + " header is not provided " +
+                                      "by the server when trying to fetch " + url);
+              }
+        
+              return connection.getInputStream();
+            }
+          });
     }
 
     @Override
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogFileOutputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogFileOutputStream.java
index f7a8b33..fb11ae0 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogFileOutputStream.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogFileOutputStream.java
@@ -176,7 +176,7 @@
    * accumulates new log records while readyBuffer will be flushed and synced.
    */
   @Override
-  public void flushAndSync() throws IOException {
+  public void flushAndSync(boolean durable) throws IOException {
     if (fp == null) {
       throw new IOException("Trying to use aborted output stream");
     }
@@ -186,7 +186,7 @@
     }
     preallocate(); // preallocate file if necessay
     doubleBuf.flushTo(fp);
-    if (!shouldSkipFsyncForTests) {
+    if (durable && !shouldSkipFsyncForTests) {
       fc.force(false); // metadata updates not needed
     }
   }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogOutputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogOutputStream.java
index cc9b62c..d5b7bff 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogOutputStream.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditLogOutputStream.java
@@ -24,6 +24,7 @@
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.jasper.compiler.JspUtil;
 
 /**
  * A generic abstract class to support journaling of edits logs into 
@@ -92,18 +93,24 @@
   /**
    * Flush and sync all data that is ready to be flush 
    * {@link #setReadyToFlush()} into underlying persistent store.
+   * @param durable if true, the edits should be made truly durable before
+   * returning
    * @throws IOException
    */
-  abstract protected void flushAndSync() throws IOException;
+  abstract protected void flushAndSync(boolean durable) throws IOException;
 
   /**
    * Flush data to persistent store.
    * Collect sync metrics.
    */
   public void flush() throws IOException {
+    flush(true);
+  }
+  
+  public void flush(boolean durable) throws IOException {
     numSync++;
     long start = now();
-    flushAndSync();
+    flushAndSync(durable);
     long end = now();
     totalTimeSync += (end - start);
   }
@@ -132,4 +139,12 @@
   protected long getNumSync() {
     return numSync;
   }
+
+  /**
+   * @return a short HTML snippet suitable for describing the current
+   * status of the stream
+   */
+  public String generateHtmlReport() {
+    return JspUtil.escapeXml(this.toString());
+  }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditsDoubleBuffer.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditsDoubleBuffer.java
index e9d22e3..d6c8a84 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditsDoubleBuffer.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EditsDoubleBuffer.java
@@ -20,6 +20,7 @@
 import java.io.IOException;
 import java.io.OutputStream;
 
+import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.hdfs.protocol.HdfsConstants;
 import org.apache.hadoop.hdfs.server.namenode.FSEditLogOp.Writer;
 import org.apache.hadoop.io.DataOutputBuffer;
@@ -34,7 +35,8 @@
  * to progress concurrently to flushes without allocating new buffers each
  * time.
  */
-class EditsDoubleBuffer {
+@InterfaceAudience.Private
+public class EditsDoubleBuffer {
 
   private TxnBuffer bufCurrent; // current buffer for writing
   private TxnBuffer bufReady; // buffer ready for flushing
@@ -51,11 +53,11 @@
     bufCurrent.writeOp(op);
   }
 
-  void writeRaw(byte[] bytes, int offset, int length) throws IOException {
+  public void writeRaw(byte[] bytes, int offset, int length) throws IOException {
     bufCurrent.write(bytes, offset, length);
   }
   
-  void close() throws IOException {
+  public void close() throws IOException {
     Preconditions.checkNotNull(bufCurrent);
     Preconditions.checkNotNull(bufReady);
 
@@ -69,7 +71,7 @@
     bufCurrent = bufReady = null;
   }
   
-  void setReadyToFlush() {
+  public void setReadyToFlush() {
     assert isFlushed() : "previous data not flushed yet";
     TxnBuffer tmp = bufReady;
     bufReady = bufCurrent;
@@ -80,12 +82,12 @@
    * Writes the content of the "ready" buffer to the given output stream,
    * and resets it. Does not swap any buffers.
    */
-  void flushTo(OutputStream out) throws IOException {
+  public void flushTo(OutputStream out) throws IOException {
     bufReady.writeTo(out); // write data to file
     bufReady.reset(); // erase all data in the buffer
   }
   
-  boolean shouldForceSync() {
+  public boolean shouldForceSync() {
     return bufCurrent.size() >= initBufferSize;
   }
 
@@ -120,6 +122,12 @@
     return bufReady.numTxns;
   }
 
+  /**
+   * @return the number of bytes that are ready to be flushed
+   */
+  public int countReadyBytes() {
+    return bufReady.size();
+  }
   
   private static class TxnBuffer extends DataOutputBuffer {
     long firstTxId;
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java
index 91ac1f6..2286e2e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java
@@ -1171,6 +1171,7 @@
       journalSet.recoverUnfinalizedSegments();
     } catch (IOException ex) {
       // All journals have failed, it is handled in logSync.
+      // TODO: are we sure this is OK?
     }
   }
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FileJournalManager.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FileJournalManager.java
index d9acff9..08ba48d 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FileJournalManager.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FileJournalManager.java
@@ -29,6 +29,7 @@
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.fs.FileUtil;
 import org.apache.hadoop.hdfs.protocol.HdfsConstants;
 import org.apache.hadoop.hdfs.server.common.Storage.StorageDirectory;
@@ -40,6 +41,7 @@
 import org.apache.hadoop.hdfs.server.protocol.RemoteEditLog;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Joiner;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 import com.google.common.collect.ComparisonChain;
@@ -51,7 +53,8 @@
  * Note: this class is not thread-safe and should be externally
  * synchronized.
  */
-class FileJournalManager implements JournalManager {
+@InterfaceAudience.Private
+public class FileJournalManager implements JournalManager {
   private static final Log LOG = LogFactory.getLog(FileJournalManager.class);
 
   private final StorageDirectory sd;
@@ -164,7 +167,7 @@
    * @return a list of remote edit logs
    * @throws IOException if edit logs cannot be listed.
    */
-  List<RemoteEditLog> getRemoteEditLogs(long firstTxId) throws IOException {
+  public List<RemoteEditLog> getRemoteEditLogs(long firstTxId) throws IOException {
     File currentDir = sd.getCurrentDir();
     List<EditLogFile> allLogFiles = matchEditLogs(currentDir);
     List<RemoteEditLog> ret = Lists.newArrayListWithCapacity(
@@ -182,6 +185,8 @@
       }
     }
     
+    Collections.sort(ret);
+    
     return ret;
   }
 
@@ -195,7 +200,7 @@
    * @throws IOException
    *           IOException thrown for invalid logDir
    */
-  static List<EditLogFile> matchEditLogs(File logDir) throws IOException {
+  public static List<EditLogFile> matchEditLogs(File logDir) throws IOException {
     return matchEditLogs(FileUtil.listFiles(logDir));
   }
   
@@ -223,7 +228,7 @@
         try {
           long startTxId = Long.valueOf(inProgressEditsMatch.group(1));
           ret.add(
-              new EditLogFile(f, startTxId, startTxId, true));
+              new EditLogFile(f, startTxId, HdfsConstants.INVALID_TXID, true));
         } catch (NumberFormatException nfe) {
           LOG.error("In-progress edits file " + f + " has improperly " +
                     "formatted transaction ID");
@@ -237,15 +242,8 @@
   @Override
   synchronized public void selectInputStreams(
       Collection<EditLogInputStream> streams, long fromTxId,
-      boolean inProgressOk) {
-    List<EditLogFile> elfs;
-    try {
-      elfs = matchEditLogs(sd.getCurrentDir());
-    } catch (IOException e) {
-      LOG.error("error listing files in " + this + ". " +
-          "Skipping all edit logs in this directory.", e);
-      return;
-    }
+      boolean inProgressOk) throws IOException {
+    List<EditLogFile> elfs = matchEditLogs(sd.getCurrentDir());
     LOG.debug(this + ": selecting input streams starting at " + fromTxId + 
         (inProgressOk ? " (inProgress ok) " : " (excluding inProgress) ") +
         "from among " + elfs.size() + " candidate file(s)");
@@ -321,7 +319,7 @@
     }
   }
 
-  List<EditLogFile> getLogFiles(long fromTxId) throws IOException {
+  public List<EditLogFile> getLogFiles(long fromTxId) throws IOException {
     File currentDir = sd.getCurrentDir();
     List<EditLogFile> allLogFiles = matchEditLogs(currentDir);
     List<EditLogFile> logFiles = Lists.newArrayList();
@@ -337,6 +335,32 @@
 
     return logFiles;
   }
+  
+  public EditLogFile getLogFile(long startTxId) throws IOException {
+    return getLogFile(sd.getCurrentDir(), startTxId);
+  }
+  
+  public static EditLogFile getLogFile(File dir, long startTxId)
+      throws IOException {
+    List<EditLogFile> files = matchEditLogs(dir);
+    List<EditLogFile> ret = Lists.newLinkedList();
+    for (EditLogFile elf : files) {
+      if (elf.getFirstTxId() == startTxId) {
+        ret.add(elf);
+      }
+    }
+    
+    if (ret.isEmpty()) {
+      // no matches
+      return null;
+    } else if (ret.size() == 1) {
+      return ret.get(0);
+    } else {
+      throw new IllegalStateException("More than one log segment in " + 
+          dir + " starting at txid " + startTxId + ": " +
+          Joiner.on(", ").join(ret));
+    }
+  }
 
   @Override
   public String toString() {
@@ -346,7 +370,8 @@
   /**
    * Record of an edit log that has been located and had its filename parsed.
    */
-  static class EditLogFile {
+  @InterfaceAudience.Private
+  public static class EditLogFile {
     private File file;
     private final long firstTxId;
     private long lastTxId;
@@ -379,17 +404,20 @@
       assert (firstTxId > 0) || (firstTxId == HdfsConstants.INVALID_TXID);
       assert file != null;
       
+      Preconditions.checkArgument(!isInProgress ||
+          lastTxId == HdfsConstants.INVALID_TXID);
+      
       this.firstTxId = firstTxId;
       this.lastTxId = lastTxId;
       this.file = file;
       this.isInProgress = isInProgress;
     }
     
-    long getFirstTxId() {
+    public long getFirstTxId() {
       return firstTxId;
     }
     
-    long getLastTxId() {
+    public long getLastTxId() {
       return lastTxId;
     }
     
@@ -402,17 +430,17 @@
      * This will update the lastTxId of the EditLogFile or
      * mark it as corrupt if it is.
      */
-    void validateLog() throws IOException {
+    public void validateLog() throws IOException {
       EditLogValidation val = EditLogFileInputStream.validateEditLog(file);
       this.lastTxId = val.getEndTxId();
       this.hasCorruptHeader = val.hasCorruptHeader();
     }
 
-    boolean isInProgress() {
+    public boolean isInProgress() {
       return isInProgress;
     }
 
-    File getFile() {
+    public File getFile() {
       return file;
     }
     
@@ -425,7 +453,7 @@
       renameSelf(".corrupt");
     }
 
-    void moveAsideEmptyFile() throws IOException {
+    public void moveAsideEmptyFile() throws IOException {
       assert lastTxId == HdfsConstants.INVALID_TXID;
       renameSelf(".empty");
     }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalManager.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalManager.java
index cda1152..872f702 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalManager.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalManager.java
@@ -65,9 +65,11 @@
    * @param inProgressOk whether or not in-progress streams should be returned
    *
    * @return a list of streams
+   * @throws IOException if the underlying storage has an error or is otherwise
+   * inaccessible
    */
   void selectInputStreams(Collection<EditLogInputStream> streams,
-      long fromTxnId, boolean inProgressOk);
+      long fromTxnId, boolean inProgressOk) throws IOException;
 
   /**
    * Set the amount of memory that this stream should use to buffer edits
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalSet.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalSet.java
index db64e63..8ed073d 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalSet.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/JournalSet.java
@@ -26,6 +26,7 @@
 import java.util.List;
 import java.util.PriorityQueue;
 import java.util.SortedSet;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -147,7 +148,7 @@
       return journal;
     }
 
-    private boolean isDisabled() {
+    boolean isDisabled() {
       return disabled;
     }
 
@@ -165,8 +166,12 @@
       return required;
     }
   }
-  
-  private List<JournalAndStream> journals = Lists.newArrayList();
+ 
+  // COW implementation is necessary since some users (eg the web ui) call
+  // getAllJournalStreams() and then iterate. Since this is rarely
+  // mutated, there is no performance concern.
+  private List<JournalAndStream> journals =
+      new CopyOnWriteArrayList<JournalSet.JournalAndStream>();
   final int minimumRedundantJournals;
   
   JournalSet(int minimumRedundantResources) {
@@ -242,8 +247,20 @@
         LOG.info("Skipping jas " + jas + " since it's disabled");
         continue;
       }
-      jas.getManager().selectInputStreams(allStreams, fromTxId, inProgressOk);
+      try {
+        jas.getManager().selectInputStreams(allStreams, fromTxId, inProgressOk);
+      } catch (IOException ioe) {
+        LOG.warn("Unable to determine input streams from " + jas.getManager() +
+            ". Skipping.", ioe);
+      }
     }
+    chainAndMakeRedundantStreams(streams, allStreams, fromTxId, inProgressOk);
+  }
+  
+  public static void chainAndMakeRedundantStreams(
+      Collection<EditLogInputStream> outStreams,
+      PriorityQueue<EditLogInputStream> allStreams,
+      long fromTxId, boolean inProgressOk) {
     // We want to group together all the streams that start on the same start
     // transaction ID.  To do this, we maintain an accumulator (acc) of all
     // the streams we've seen at a given start transaction ID.  When we see a
@@ -261,7 +278,7 @@
         if (accFirstTxId == elis.getFirstTxId()) {
           acc.add(elis);
         } else if (accFirstTxId < elis.getFirstTxId()) {
-          streams.add(new RedundantEditLogInputStream(acc, fromTxId));
+          outStreams.add(new RedundantEditLogInputStream(acc, fromTxId));
           acc.clear();
           acc.add(elis);
         } else if (accFirstTxId > elis.getFirstTxId()) {
@@ -272,7 +289,7 @@
       }
     }
     if (!acc.isEmpty()) {
-      streams.add(new RedundantEditLogInputStream(acc, fromTxId));
+      outStreams.add(new RedundantEditLogInputStream(acc, fromTxId));
       acc.clear();
     }
   }
@@ -454,12 +471,12 @@
     }
 
     @Override
-    protected void flushAndSync() throws IOException {
+    protected void flushAndSync(final boolean durable) throws IOException {
       mapJournalsAndReportErrors(new JournalClosure() {
         @Override
         public void apply(JournalAndStream jas) throws IOException {
           if (jas.isActive()) {
-            jas.getCurrentStream().flushAndSync();
+            jas.getCurrentStream().flushAndSync(durable);
           }
         }
       }, "flushAndSync");
@@ -512,7 +529,6 @@
     }
   }
   
-  @VisibleForTesting
   List<JournalAndStream> getAllJournalStreams() {
     return journals;
   }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNode.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNode.java
index 616e843..fb5c88d 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNode.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNode.java
@@ -722,6 +722,12 @@
     String namenodeId = HAUtil.getNameNodeId(conf, nsId);
     initializeGenericKeys(conf, nsId, namenodeId);
     checkAllowFormat(conf);
+
+    if (UserGroupInformation.isSecurityEnabled()) {
+      InetSocketAddress socAddr = getAddress(conf);
+      SecurityUtil.login(conf, DFS_NAMENODE_KEYTAB_FILE_KEY,
+          DFS_NAMENODE_USER_NAME_KEY, socAddr.getHostName());
+    }
     
     Collection<URI> nameDirsToFormat = FSNamesystem.getNamespaceDirs(conf);
     List<URI> sharedDirs = FSNamesystem.getSharedEditsDirs(conf);
@@ -763,13 +769,13 @@
   }
   
   @VisibleForTesting
-  public static boolean initializeSharedEdits(Configuration conf) {
+  public static boolean initializeSharedEdits(Configuration conf) throws IOException {
     return initializeSharedEdits(conf, true);
   }
   
   @VisibleForTesting
   public static boolean initializeSharedEdits(Configuration conf,
-      boolean force) {
+      boolean force) throws IOException {
     return initializeSharedEdits(conf, force, false);
   }
 
@@ -783,7 +789,7 @@
    * @return true if the command aborts, false otherwise
    */
   private static boolean initializeSharedEdits(Configuration conf,
-      boolean force, boolean interactive) {
+      boolean force, boolean interactive) throws IOException {
     String nsId = DFSUtil.getNamenodeNameServiceId(conf);
     String namenodeId = HAUtil.getNameNodeId(conf, nsId);
     initializeGenericKeys(conf, nsId, namenodeId);
@@ -794,6 +800,12 @@
       return false;
     }
 
+    if (UserGroupInformation.isSecurityEnabled()) {
+      InetSocketAddress socAddr = getAddress(conf);
+      SecurityUtil.login(conf, DFS_NAMENODE_KEYTAB_FILE_KEY,
+          DFS_NAMENODE_USER_NAME_KEY, socAddr.getHostName());
+    }
+
     NNStorage existingStorage = null;
     try {
       Configuration confWithoutShared = new Configuration(conf);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeResourcePolicy.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeResourcePolicy.java
index 3896165..03f226c 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeResourcePolicy.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeResourcePolicy.java
@@ -41,6 +41,14 @@
   static boolean areResourcesAvailable(
       Collection<? extends CheckableNameNodeResource> resources,
       int minimumRedundantResources) {
+
+    // TODO: workaround:
+    // - during startup, if there are no edits dirs on disk, then there is
+    // a call to areResourcesAvailable() with no dirs at all, which was
+    // previously causing the NN to enter safemode
+    if (resources.isEmpty()) {
+      return true;
+    }
     
     int requiredResourceCount = 0;
     int redundantResourceCount = 0;
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeJspHelper.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeJspHelper.java
index 1ffb343..07f3f5f 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeJspHelper.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NamenodeJspHelper.java
@@ -48,6 +48,7 @@
 import org.apache.hadoop.hdfs.server.common.JspHelper;
 import org.apache.hadoop.hdfs.server.common.Storage;
 import org.apache.hadoop.hdfs.server.common.Storage.StorageDirectory;
+import org.apache.hadoop.hdfs.server.namenode.JournalSet.JournalAndStream;
 import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocols;
 import org.apache.hadoop.http.HttpConfig;
 import org.apache.hadoop.io.Text;
@@ -60,6 +61,8 @@
 import org.apache.hadoop.util.VersionInfo;
 import org.znerd.xmlenc.XMLOutputter;
 
+import com.google.common.base.Preconditions;
+
 class NamenodeJspHelper {
   static String getSafeModeText(FSNamesystem fsn) {
     if (!fsn.isInSafeMode())
@@ -212,6 +215,52 @@
 
       out.print("</table></div>\n");
     }
+    
+    /**
+     * Generate an HTML report containing the current status of the HDFS
+     * journals.
+     */
+    void generateJournalReport(JspWriter out, NameNode nn,
+        HttpServletRequest request) throws IOException {
+      FSEditLog log = nn.getFSImage().getEditLog();
+      Preconditions.checkArgument(log != null, "no edit log set in %s", nn);
+      
+      out.println("<h3> " + nn.getRole() + " Journal Status: </h3>");
+
+      out.println("<b>Current transaction ID:</b> " +
+          nn.getFSImage().getLastAppliedOrWrittenTxId() + "<br/>");
+      
+      
+      boolean openForWrite = log.isOpenForWrite();
+      
+      out.println("<div class=\"dfstable\">");
+      out.println("<table class=\"storage\" title=\"NameNode Journals\">\n"
+              + "<thead><tr><td><b>Journal Manager</b></td><td><b>State</b></td></tr></thead>");
+      for (JournalAndStream jas : log.getJournals()) {
+        out.print("<tr>");
+        out.print("<td>" + jas.getManager());
+        if (jas.isRequired()) {
+          out.print(" [required]");
+        }
+        out.print("</td><td>");
+        
+        if (jas.isDisabled()) {
+          out.print("<span class=\"failed\">Failed</span>");
+        } else if (openForWrite) {
+          EditLogOutputStream elos = jas.getCurrentStream();
+          if (elos != null) {
+            out.println(elos.generateHtmlReport());
+          } else {
+            out.println("not currently writing");
+          }
+        } else {
+          out.println("open for read");
+        }
+        out.println("</td></tr>");
+      }
+      
+      out.println("</table></div>");
+    }
 
     void generateHealthReport(JspWriter out, NameNode nn,
         HttpServletRequest request) throws IOException {
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/EditLogTailer.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/EditLogTailer.java
index a403706..8e0739a 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/EditLogTailer.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/EditLogTailer.java
@@ -21,6 +21,7 @@
 import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.security.PrivilegedAction;
+import java.security.PrivilegedExceptionAction;
 import java.util.Collection;
 
 import org.apache.commons.logging.Log;
@@ -172,11 +173,20 @@
     Preconditions.checkState(tailerThread == null ||
         !tailerThread.isAlive(),
         "Tailer thread should not be running once failover starts");
-    try {
-      doTailEdits();
-    } catch (InterruptedException e) {
-      throw new IOException(e);
-    }
+    // Important to do tailing as the login user, in case the shared
+    // edits storage is implemented by a JournalManager that depends
+    // on security credentials to access the logs (eg QuorumJournalManager).
+    SecurityUtil.doAsLoginUser(new PrivilegedExceptionAction<Void>() {
+      @Override
+      public Void run() throws Exception {
+        try {
+          doTailEdits();
+        } catch (InterruptedException e) {
+          throw new IOException(e);
+        }
+        return null;
+      }
+    });
   }
   
   @VisibleForTesting
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/RemoteEditLog.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/RemoteEditLog.java
index b6f5887..68fad56 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/RemoteEditLog.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/RemoteEditLog.java
@@ -17,18 +17,15 @@
  */
 package org.apache.hadoop.hdfs.server.protocol;
 
-import java.io.DataInput;
-import java.io.DataOutput;
-import java.io.IOException;
 import org.apache.hadoop.hdfs.protocol.HdfsConstants;
-import org.apache.hadoop.io.Writable;
 
 import com.google.common.base.Function;
 import com.google.common.collect.ComparisonChain;
 
-public class RemoteEditLog implements Writable, Comparable<RemoteEditLog> {
+public class RemoteEditLog implements Comparable<RemoteEditLog> {
   private long startTxId = HdfsConstants.INVALID_TXID;
   private long endTxId = HdfsConstants.INVALID_TXID;
+  private boolean isInProgress = false;
   
   public RemoteEditLog() {
   }
@@ -36,6 +33,13 @@
   public RemoteEditLog(long startTxId, long endTxId) {
     this.startTxId = startTxId;
     this.endTxId = endTxId;
+    this.isInProgress = (endTxId == HdfsConstants.INVALID_TXID);
+  }
+  
+  public RemoteEditLog(long startTxId, long endTxId, boolean inProgress) {
+    this.startTxId = startTxId;
+    this.endTxId = endTxId;
+    this.isInProgress = inProgress;
   }
 
   public long getStartTxId() {
@@ -45,22 +49,18 @@
   public long getEndTxId() {
     return endTxId;
   }
-    
+
+  public boolean isInProgress() {
+    return isInProgress;
+  }
+
   @Override
   public String toString() {
-    return "[" + startTxId + "," + endTxId + "]";
-  }
-
-  @Override
-  public void write(DataOutput out) throws IOException {
-    out.writeLong(startTxId);
-    out.writeLong(endTxId);
-  }
-
-  @Override
-  public void readFields(DataInput in) throws IOException {
-    startTxId = in.readLong();
-    endTxId = in.readLong();
+    if (!isInProgress) {
+      return "[" + startTxId + "," + endTxId + "]";
+    } else {
+      return "[" + startTxId + "-? (in-progress)]";
+    }
   }
   
   @Override
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/RemoteEditLogManifest.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/RemoteEditLogManifest.java
index 60e41a6..0b3a031 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/RemoteEditLogManifest.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/RemoteEditLogManifest.java
@@ -40,8 +40,8 @@
   
   
   /**
-   * Check that the logs are contiguous and non-overlapping
-   * sequences of transactions, in sorted order
+   * Check that the logs are non-overlapping sequences of transactions,
+   * in sorted order. They do not need to be contiguous.
    * @throws IllegalStateException if incorrect
    */
   private void checkState()  {
@@ -50,8 +50,10 @@
     RemoteEditLog prev = null;
     for (RemoteEditLog log : logs) {
       if (prev != null) {
-        if (log.getStartTxId() != prev.getEndTxId() + 1) {
-          throw new IllegalStateException("Invalid log manifest:" + this);
+        if (log.getStartTxId() <= prev.getEndTxId()) {
+          throw new IllegalStateException(
+              "Invalid log manifest (log " + log + " overlaps " + prev + ")\n"
+              + this);
         }
       }
       
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/offlineEditsViewer/BinaryEditsVisitor.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/offlineEditsViewer/BinaryEditsVisitor.java
index 1911ef7..8c4fcbb 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/offlineEditsViewer/BinaryEditsVisitor.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/offlineEditsViewer/BinaryEditsVisitor.java
@@ -56,7 +56,7 @@
   @Override
   public void close(Throwable error) throws IOException {
     elfos.setReadyToFlush();
-    elfos.flushAndSync();
+    elfos.flushAndSync(true);
     elfos.close();
   }
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/BestEffortLongFile.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/BestEffortLongFile.java
new file mode 100644
index 0000000..292402b
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/BestEffortLongFile.java
@@ -0,0 +1,117 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.util;
+
+import java.io.Closeable;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.io.IOUtils;
+
+import com.google.common.io.Files;
+import com.google.common.primitives.Longs;
+
+/**
+ * Class that represents a file on disk which stores a single <code>long</code>
+ * value, but does not make any effort to make it truly durable. This is in
+ * contrast to {@link PersistentLongFile} which fsync()s the value on every
+ * change.
+ * 
+ * This should be used for values which are updated frequently (such that
+ * performance is important) and not required to be up-to-date for correctness.
+ * 
+ * This class also differs in that it stores the value as binary data instead
+ * of a textual string.
+ */
+@InterfaceAudience.Private
+public class BestEffortLongFile implements Closeable {
+
+  private final File file;
+  private final long defaultVal;
+
+  private long value;
+  
+  private FileChannel ch = null;
+  
+  private ByteBuffer buf = ByteBuffer.allocate(Long.SIZE/8);
+  
+  public BestEffortLongFile(File file, long defaultVal) {
+    this.file = file;
+    this.defaultVal = defaultVal;
+  }
+  
+  public long get() throws IOException {
+    lazyOpen();
+    return value;
+  }
+
+  public void set(long newVal) throws IOException {
+    lazyOpen();
+    buf.clear();
+    buf.putLong(newVal);
+    buf.flip();
+    IOUtils.writeFully(ch, buf, 0);
+    value = newVal;
+  }
+  
+  private void lazyOpen() throws IOException {
+    if (ch != null) {
+      return;
+    }
+
+    // Load current value.
+    byte[] data = null;
+    try {
+      data = Files.toByteArray(file);
+    } catch (FileNotFoundException fnfe) {
+      // Expected - this will use default value.
+    }
+
+    if (data != null && data.length != 0) {
+      if (data.length != Longs.BYTES) {
+        throw new IOException("File " + file + " had invalid length: " +
+            data.length);
+      }
+      value = Longs.fromByteArray(data);
+    } else {
+      value = defaultVal;
+    }
+    
+    // Now open file for future writes.
+    RandomAccessFile raf = new RandomAccessFile(file, "rw");
+    try {
+      ch = raf.getChannel();
+    } finally {
+      if (ch == null) {
+        IOUtils.closeStream(raf);
+      }
+    }
+  }
+  
+  @Override
+  public void close() throws IOException {
+    if (ch != null) {
+      ch.close();
+    }
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/PersistentLongFile.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/PersistentLongFile.java
index 5e77622..292d0df 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/PersistentLongFile.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/PersistentLongFile.java
@@ -57,7 +57,9 @@
   }
   
   public void set(long newVal) throws IOException {
-    writeFile(file, newVal);
+    if (value != newVal || !loaded) {
+      writeFile(file, newVal);
+    }
     value = newVal;
     loaded = true;
   }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/QJournalProtocol.proto b/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/QJournalProtocol.proto
new file mode 100644
index 0000000..d188f2b
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/QJournalProtocol.proto
@@ -0,0 +1,252 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+option java_package = "org.apache.hadoop.hdfs.qjournal.protocol";
+option java_outer_classname = "QJournalProtocolProtos";
+option java_generic_services = true;
+option java_generate_equals_and_hash = true;
+
+import "hdfs.proto";
+
+message JournalIdProto {
+  required string identifier = 1;
+}
+
+message RequestInfoProto {
+  required JournalIdProto journalId = 1;
+  required uint64 epoch = 2;
+  required uint64 ipcSerialNumber = 3;
+
+  // Whenever a writer makes a request, it informs
+  // the node of the latest committed txid. This may
+  // be higher than the transaction data included in the
+  // request itself, eg in the case that the node has
+  // fallen behind.
+  optional uint64 committedTxId = 4;
+}
+
+message SegmentStateProto {
+  required uint64 startTxId = 1;
+  required uint64 endTxId = 2;
+  required bool isInProgress = 3;
+}
+
+/**
+ * The storage format used on local disk for previously
+ * accepted decisions.
+ */
+message PersistedRecoveryPaxosData {
+  required SegmentStateProto segmentState = 1;
+  required uint64 acceptedInEpoch = 2;
+}
+
+/**
+ * journal()
+ */
+
+message JournalRequestProto {
+  required RequestInfoProto reqInfo = 1;
+  required uint64 firstTxnId = 2;
+  required uint32 numTxns = 3;
+  required bytes records = 4;
+  required uint64 segmentTxnId = 5;
+}
+
+message JournalResponseProto { 
+}
+
+/**
+ * heartbeat()
+ */
+
+message HeartbeatRequestProto {
+  required RequestInfoProto reqInfo = 1;
+}
+
+message HeartbeatResponseProto { // void response
+}
+
+/**
+ * startLogSegment()
+ */
+message StartLogSegmentRequestProto {
+  required RequestInfoProto reqInfo = 1;
+  required uint64 txid = 2; // Transaction ID
+}
+
+message StartLogSegmentResponseProto { 
+}
+
+/**
+ * finalizeLogSegment()
+ */
+message FinalizeLogSegmentRequestProto {
+  required RequestInfoProto reqInfo = 1;
+  required uint64 startTxId = 2;
+  required uint64 endTxId = 3;
+}
+
+message FinalizeLogSegmentResponseProto { 
+}
+
+/**
+ * purgeLogs()
+ */
+message PurgeLogsRequestProto {
+  required RequestInfoProto reqInfo = 1;
+  required uint64 minTxIdToKeep = 2;
+}
+
+message PurgeLogsResponseProto {
+}
+
+/**
+ * isFormatted()
+ */
+message IsFormattedRequestProto {
+  required JournalIdProto jid = 1;
+}
+
+message IsFormattedResponseProto {
+  required bool isFormatted = 1;
+}
+
+/**
+ * getJournalState()
+ */
+message GetJournalStateRequestProto {
+  required JournalIdProto jid = 1;
+}
+
+message GetJournalStateResponseProto {
+  required uint64 lastPromisedEpoch = 1;
+  required uint32 httpPort = 2;
+}
+
+/**
+ * format()
+ */
+message FormatRequestProto {
+  required JournalIdProto jid = 1;
+  required NamespaceInfoProto nsInfo = 2;
+}
+
+message FormatResponseProto {
+}
+
+/**
+ * newEpoch()
+ */
+message NewEpochRequestProto {
+  required JournalIdProto jid = 1;
+  required NamespaceInfoProto nsInfo = 2;
+  required uint64 epoch = 3;
+}
+
+message NewEpochResponseProto {
+  optional uint64 lastSegmentTxId = 1;
+}
+
+/**
+ * getEditLogManifest()
+ */
+message GetEditLogManifestRequestProto {
+  required JournalIdProto jid = 1;
+  required uint64 sinceTxId = 2;  // Transaction ID
+}
+
+message GetEditLogManifestResponseProto {
+  required RemoteEditLogManifestProto manifest = 1; 
+  required uint32 httpPort = 2;
+
+  // TODO: we should add nsinfo somewhere
+  // to verify that it matches up with our expectation
+  // required NamespaceInfoProto nsInfo = 2;
+}
+
+/**
+ * prepareRecovery()
+ */
+message PrepareRecoveryRequestProto {
+  required RequestInfoProto reqInfo = 1;
+  required uint64 segmentTxId = 2;
+}
+
+message PrepareRecoveryResponseProto {
+  optional SegmentStateProto segmentState = 1;
+  optional uint64 acceptedInEpoch = 2;
+  required uint64 lastWriterEpoch = 3;
+
+  // The highest committed txid that this logger has ever seen.
+  // This may be higher than the data it actually has, in the case
+  // that it was lagging before the old writer crashed.
+  optional uint64 lastCommittedTxId = 4;
+}
+
+/**
+ * acceptRecovery()
+ */
+message AcceptRecoveryRequestProto {
+  required RequestInfoProto reqInfo = 1;
+
+  /** Details on the segment to recover */
+  required SegmentStateProto stateToAccept = 2;
+  
+  /** The URL from which the log may be copied */
+  required string fromURL = 3;
+}
+
+message AcceptRecoveryResponseProto {
+}
+
+
+/**
+ * Protocol used to journal edits to a JournalNode.
+ * See the request and response for details of rpc call.
+ */
+service QJournalProtocolService {
+  rpc isFormatted(IsFormattedRequestProto) returns (IsFormattedResponseProto);
+
+  rpc getJournalState(GetJournalStateRequestProto) returns (GetJournalStateResponseProto);
+
+  rpc newEpoch(NewEpochRequestProto) returns (NewEpochResponseProto);
+
+  rpc format(FormatRequestProto) returns (FormatResponseProto);
+
+  rpc journal(JournalRequestProto) returns (JournalResponseProto);
+
+  rpc heartbeat(HeartbeatRequestProto) returns (HeartbeatResponseProto);
+
+  rpc startLogSegment(StartLogSegmentRequestProto) 
+      returns (StartLogSegmentResponseProto);
+
+  rpc finalizeLogSegment(FinalizeLogSegmentRequestProto)
+      returns (FinalizeLogSegmentResponseProto);
+
+  rpc purgeLogs(PurgeLogsRequestProto)
+      returns (PurgeLogsResponseProto);
+
+  rpc getEditLogManifest(GetEditLogManifestRequestProto)
+      returns (GetEditLogManifestResponseProto);
+
+  rpc prepareRecovery(PrepareRecoveryRequestProto)
+      returns (PrepareRecoveryResponseProto);
+
+  rpc acceptRecovery(AcceptRecoveryRequestProto)
+      returns (AcceptRecoveryResponseProto);
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/hdfs.proto b/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/hdfs.proto
index 70a0475..924fc01 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/hdfs.proto
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/proto/hdfs.proto
@@ -302,6 +302,7 @@
 message RemoteEditLogProto {
   required uint64 startTxId = 1;  // Starting available edit log transaction
   required uint64 endTxId = 2;    // Ending available edit log transaction
+  optional bool isInProgress = 3 [default = false];
 }
 
 /**
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml b/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml
index ae9f500..153e21b 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml
@@ -260,6 +260,11 @@
 </property>
 
 <property>
+  <name>dfs.namenode.edits.journal-plugin.qjournal</name>
+  <value>org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager</value>
+</property>
+
+<property>
   <name>dfs.permissions.enabled</name>
   <value>true</value>
   <description>
@@ -1118,4 +1123,21 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.journalnode.rpc-address</name>
+  <value>0.0.0.0:8485</value>
+  <description>
+    The JournalNode RPC server address and port.
+  </description>
+</property>
+
+<property>
+  <name>dfs.journalnode.http-address</name>
+  <value>0.0.0.0:8480</value>
+  <description>
+    The address and port the JournalNode web UI listens on.
+    If the port is 0 then the server will start on a free port.
+  </description>
+</property>
+
 </configuration>
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/hdfs/dfshealth.jsp b/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/hdfs/dfshealth.jsp
index 3affe6b..a89e036 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/hdfs/dfshealth.jsp
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/hdfs/dfshealth.jsp
@@ -60,8 +60,10 @@
 <%= NamenodeJspHelper.getCorruptFilesWarning(fsn)%>
 
 <% healthjsp.generateHealthReport(out, nn, request); %>
-<hr>
+<% healthjsp.generateJournalReport(out, nn, request); %>
+<hr/>
 <% healthjsp.generateConfReport(out, nn, request); %>
+<hr>
 <%
 out.println(ServletUtil.htmlFooter());
 %>
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/journal/index.html b/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/journal/index.html
new file mode 100644
index 0000000..bc9ea42
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/journal/index.html
@@ -0,0 +1,29 @@
+<meta HTTP-EQUIV="REFRESH" content="0;url=journalstatus.jsp"/>
+<html>
+<!--
+   Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed with
+   this work for additional information regarding copyright ownership.
+   The ASF licenses this file to You under the Apache License, Version 2.0
+   (the "License"); you may not use this file except in compliance with
+   the License.  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+-->
+<head><title>Hadoop Administration</title></head>
+
+<body>
+<h1>Hadoop Administration</h1>
+
+<ul> 
+  <li><a href="journalstatus.jsp">Status</a></li> 
+</ul>
+
+</body> 
+</html>
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/journal/journalstatus.jsp b/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/journal/journalstatus.jsp
new file mode 100644
index 0000000..2c6e5a3
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/journal/journalstatus.jsp
@@ -0,0 +1,42 @@
+<%
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file 
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+%>
+<%@ page
+  contentType="text/html; charset=UTF-8"
+  import="org.apache.hadoop.hdfs.server.common.JspHelper"
+  import="org.apache.hadoop.util.ServletUtil"
+%>
+<%!
+  //for java.io.Serializable
+  private static final long serialVersionUID = 1L;
+%>
+
+<!DOCTYPE html>
+<html>
+<link rel="stylesheet" type="text/css" href="/static/hadoop.css">
+<title>Hadoop JournalNode</title>
+    
+<body>
+<h1>JournalNode</h1>
+<%= JspHelper.getVersionTable() %>
+<hr />
+
+<br />
+<b><a href="/logs/">Logs</a></b>
+<%= ServletUtil.htmlFooter() %>
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/proto-journal-web.xml b/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/proto-journal-web.xml
new file mode 100644
index 0000000..b27f82b
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/proto-journal-web.xml
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License. See accompanying LICENSE file.
+-->
+<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee">
+@journal.servlet.definitions@
+</web-app>
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/DFSTestUtil.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/DFSTestUtil.java
index 6f862a3..3e1451c 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/DFSTestUtil.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/DFSTestUtil.java
@@ -85,6 +85,7 @@
 import org.apache.hadoop.security.token.Token;
 import org.apache.hadoop.util.VersionInfo;
 
+import com.google.common.base.Charsets;
 import com.google.common.base.Joiner;
 
 /** Utilities for HDFS tests */
@@ -607,12 +608,21 @@
     IOUtils.copyBytes(is, os, s.length(), true);
   }
   
-  // Returns url content as string.
+  /**
+   * @return url content as string (UTF-8 encoding assumed)
+   */
   public static String urlGet(URL url) throws IOException {
+    return new String(urlGetBytes(url), Charsets.UTF_8);
+  }
+  
+  /**
+   * @return URL contents as a byte array
+   */
+  public static byte[] urlGetBytes(URL url) throws IOException {
     URLConnection conn = url.openConnection();
     ByteArrayOutputStream out = new ByteArrayOutputStream();
     IOUtils.copyBytes(conn.getInputStream(), out, 4096, true);
-    return out.toString();
+    return out.toByteArray();
   }
   
   /**
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/MiniJournalCluster.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/MiniJournalCluster.java
new file mode 100644
index 0000000..840f493
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/MiniJournalCluster.java
@@ -0,0 +1,194 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.util.List;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileUtil;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.qjournal.server.JournalNode;
+
+import com.google.common.base.Joiner;
+import com.google.common.collect.Lists;
+
+public class MiniJournalCluster {
+  public static class Builder {
+    private String baseDir;
+    private int numJournalNodes = 3;
+    private boolean format = true;
+    private Configuration conf;
+    
+    public Builder(Configuration conf) {
+      this.conf = conf;
+    }
+    
+    public Builder baseDir(String d) {
+      this.baseDir = d;
+      return this;
+    }
+    
+    public Builder numJournalNodes(int n) {
+      this.numJournalNodes = n;
+      return this;
+    }
+
+    public Builder format(boolean f) {
+      this.format = f;
+      return this;
+    }
+
+    public MiniJournalCluster build() throws IOException {
+      return new MiniJournalCluster(this);
+    }
+  }
+
+  private static final Log LOG = LogFactory.getLog(MiniJournalCluster.class);
+  private File baseDir;
+  private JournalNode nodes[];
+  private InetSocketAddress ipcAddrs[];
+  private InetSocketAddress httpAddrs[];
+  
+  private MiniJournalCluster(Builder b) throws IOException {
+    LOG.info("Starting MiniJournalCluster with " +
+        b.numJournalNodes + " journal nodes");
+    
+    if (b.baseDir != null) {
+      this.baseDir = new File(b.baseDir);
+    } else {
+      this.baseDir = new File(MiniDFSCluster.getBaseDirectory());
+    }
+    
+    nodes = new JournalNode[b.numJournalNodes];
+    ipcAddrs = new InetSocketAddress[b.numJournalNodes];
+    httpAddrs = new InetSocketAddress[b.numJournalNodes];
+    for (int i = 0; i < b.numJournalNodes; i++) {
+      if (b.format) {
+        File dir = getStorageDir(i);
+        LOG.debug("Fully deleting JN directory " + dir);
+        FileUtil.fullyDelete(dir);
+      }
+      nodes[i] = new JournalNode();
+      nodes[i].setConf(createConfForNode(b, i));
+      nodes[i].start();
+
+      ipcAddrs[i] = nodes[i].getBoundIpcAddress();
+      httpAddrs[i] = nodes[i].getBoundHttpAddress();
+    }
+  }
+
+  /**
+   * Set up the given Configuration object to point to the set of JournalNodes 
+   * in this cluster.
+   */
+  public URI getQuorumJournalURI(String jid) {
+    List<String> addrs = Lists.newArrayList();
+    for (InetSocketAddress addr : ipcAddrs) {
+      addrs.add("127.0.0.1:" + addr.getPort());
+    }
+    String addrsVal = Joiner.on(";").join(addrs);
+    LOG.debug("Setting logger addresses to: " + addrsVal);
+    try {
+      return new URI("qjournal://" + addrsVal + "/" + jid);
+    } catch (URISyntaxException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  /**
+   * Start the JournalNodes in the cluster.
+   */
+  public void start() throws IOException {
+    for (JournalNode jn : nodes) {
+      jn.start();
+    }
+  }
+
+  /**
+   * Shutdown all of the JournalNodes in the cluster.
+   * @throws IOException if one or more nodes failed to stop
+   */
+  public void shutdown() throws IOException {
+    boolean failed = false;
+    for (JournalNode jn : nodes) {
+      try {
+        jn.stopAndJoin(0);
+      } catch (Exception e) {
+        failed = true;
+        LOG.warn("Unable to stop journal node " + jn, e);
+      }
+    }
+    if (failed) {
+      throw new IOException("Unable to shut down. Check log for details");
+    }
+  }
+
+  private Configuration createConfForNode(Builder b, int idx) {
+    Configuration conf = new Configuration(b.conf);
+    File logDir = getStorageDir(idx);
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_KEY, logDir.toString());
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_RPC_ADDRESS_KEY, "0.0.0.0:0");
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_HTTP_ADDRESS_KEY, "0.0.0.0:0");
+    return conf;
+  }
+
+  public File getStorageDir(int idx) {
+    return new File(baseDir, "journalnode-" + idx).getAbsoluteFile();
+  }
+  
+  public File getCurrentDir(int idx, String jid) {
+    return new File(new File(getStorageDir(idx), jid), "current");
+  }
+
+  public JournalNode getJournalNode(int i) {
+    return nodes[i];
+  }
+  
+  public void restartJournalNode(int i) throws InterruptedException, IOException {
+    Configuration conf = new Configuration(nodes[i].getConf());
+    if (nodes[i].isStarted()) {
+      nodes[i].stopAndJoin(0);
+    }
+    
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_RPC_ADDRESS_KEY, "127.0.0.1:" +
+        ipcAddrs[i].getPort());
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_HTTP_ADDRESS_KEY, "127.0.0.1:" +
+        httpAddrs[i].getPort());
+    
+    JournalNode jn = new JournalNode();
+    jn.setConf(conf);
+    jn.start();
+  }
+
+  public int getQuorumSize() {
+    return nodes.length / 2 + 1;
+  }
+
+  public int getNumNodes() {
+    return nodes.length;
+  }
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/QJMTestUtil.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/QJMTestUtil.java
new file mode 100644
index 0000000..f06f62e
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/QJMTestUtil.java
@@ -0,0 +1,161 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import java.io.Closeable;
+import java.io.File;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+
+import org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager;
+import org.apache.hadoop.hdfs.server.namenode.EditLogInputStream;
+import org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream;
+import org.apache.hadoop.hdfs.server.namenode.FSEditLogOp;
+import org.apache.hadoop.hdfs.server.namenode.FSEditLogOpCodes;
+import org.apache.hadoop.hdfs.server.namenode.NNStorage;
+import org.apache.hadoop.hdfs.server.namenode.NameNodeAdapter;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.io.DataOutputBuffer;
+import org.apache.hadoop.io.IOUtils;
+
+import com.google.common.collect.Lists;
+
+public abstract class QJMTestUtil {
+  public static final NamespaceInfo FAKE_NSINFO = new NamespaceInfo(
+      12345, "mycluster", "my-bp", 0L);
+  public static final String JID = "test-journal";
+
+  public static byte[] createTxnData(int startTxn, int numTxns) throws Exception {
+    DataOutputBuffer buf = new DataOutputBuffer();
+    FSEditLogOp.Writer writer = new FSEditLogOp.Writer(buf);
+    
+    for (long txid = startTxn; txid < startTxn + numTxns; txid++) {
+      FSEditLogOp op = NameNodeAdapter.createMkdirOp("tx " + txid);
+      op.setTransactionId(txid);
+      writer.writeOp(op);
+    }
+    
+    return Arrays.copyOf(buf.getData(), buf.getLength());
+  }
+  
+  public static EditLogOutputStream writeSegment(MiniJournalCluster cluster,
+      QuorumJournalManager qjm, long startTxId, int numTxns,
+      boolean finalize) throws IOException {
+    EditLogOutputStream stm = qjm.startLogSegment(startTxId);
+    // Should create in-progress
+    assertExistsInQuorum(cluster,
+        NNStorage.getInProgressEditsFileName(startTxId));
+    
+    writeTxns(stm, startTxId, numTxns);
+    if (finalize) {
+      stm.close();
+      qjm.finalizeLogSegment(startTxId, startTxId + numTxns - 1);
+      return null;
+    } else {
+      return stm;
+    }
+  }
+
+  public static void writeOp(EditLogOutputStream stm, long txid) throws IOException {
+    FSEditLogOp op = NameNodeAdapter.createMkdirOp("tx " + txid);
+    op.setTransactionId(txid);
+    stm.write(op);
+  }
+
+  public static void writeTxns(EditLogOutputStream stm, long startTxId, int numTxns)
+      throws IOException {
+    for (long txid = startTxId; txid < startTxId + numTxns; txid++) {
+      writeOp(stm, txid);
+    }
+    stm.setReadyToFlush();
+    stm.flush();
+  }
+  
+  /**
+   * Verify that the given list of streams contains exactly the range of
+   * transactions specified, inclusive.
+   */
+  public static void verifyEdits(List<EditLogInputStream> streams,
+      int firstTxnId, int lastTxnId) throws IOException {
+    
+    Iterator<EditLogInputStream> iter = streams.iterator();
+    assertTrue(iter.hasNext());
+    EditLogInputStream stream = iter.next();
+    
+    for (int expected = firstTxnId;
+        expected <= lastTxnId;
+        expected++) {
+      
+      FSEditLogOp op = stream.readOp();
+      while (op == null) {
+        assertTrue("Expected to find txid " + expected + ", " +
+            "but no more streams available to read from",
+            iter.hasNext());
+        stream = iter.next();
+        op = stream.readOp();
+      }
+      
+      assertEquals(FSEditLogOpCodes.OP_MKDIR, op.opCode);
+      assertEquals(expected, op.getTransactionId());
+    }
+    
+    assertNull(stream.readOp());
+    assertFalse("Expected no more txns after " + lastTxnId +
+        " but more streams are available", iter.hasNext());
+  }
+  
+
+  public static void assertExistsInQuorum(MiniJournalCluster cluster,
+      String fname) {
+    int count = 0;
+    for (int i = 0; i < 3; i++) {
+      File dir = cluster.getCurrentDir(i, JID);
+      if (new File(dir, fname).exists()) {
+        count++;
+      }
+    }
+    assertTrue("File " + fname + " should exist in a quorum of dirs",
+        count >= cluster.getQuorumSize());
+  }
+
+  public static long recoverAndReturnLastTxn(QuorumJournalManager qjm)
+      throws IOException {
+    qjm.recoverUnfinalizedSegments();
+    long lastRecoveredTxn = 0;
+
+    List<EditLogInputStream> streams = Lists.newArrayList();
+    try {
+      qjm.selectInputStreams(streams, 0, false);
+      
+      for (EditLogInputStream elis : streams) {
+        assertTrue(elis.getFirstTxId() > lastRecoveredTxn);
+        lastRecoveredTxn = elis.getLastTxId();
+      }
+    } finally {
+      IOUtils.cleanup(null, streams.toArray(new Closeable[0]));
+    }
+    return lastRecoveredTxn;
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/TestMiniJournalCluster.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/TestMiniJournalCluster.java
new file mode 100644
index 0000000..fbb51e1
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/TestMiniJournalCluster.java
@@ -0,0 +1,54 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal;
+
+import static org.junit.Assert.*;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URI;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.qjournal.server.JournalNode;
+import org.junit.Test;
+
+
+public class TestMiniJournalCluster {
+  @Test
+  public void testStartStop() throws IOException {
+    Configuration conf = new Configuration();
+    MiniJournalCluster c = new MiniJournalCluster.Builder(conf)
+      .build();
+    try {
+      URI uri = c.getQuorumJournalURI("myjournal");
+      String[] addrs = uri.getAuthority().split(";");
+      assertEquals(3, addrs.length);
+      
+      JournalNode node = c.getJournalNode(0);
+      String dir = node.getConf().get(DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_KEY);
+      assertEquals(
+          new File(MiniDFSCluster.getBaseDirectory() + "journalnode-0")
+            .getAbsolutePath(),
+          dir);
+    } finally {
+      c.shutdown();
+    }
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/TestNNWithQJM.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/TestNNWithQJM.java
new file mode 100644
index 0000000..a5463d0
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/TestNNWithQJM.java
@@ -0,0 +1,242 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal;
+
+import static org.junit.Assert.*;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URL;
+import java.util.regex.Pattern;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.FileUtil;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.DFSTestUtil;
+import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.server.namenode.NameNode;
+import org.apache.hadoop.ipc.RemoteException;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.apache.hadoop.util.ExitUtil;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+public class TestNNWithQJM {
+  Configuration conf = new HdfsConfiguration();
+  private MiniJournalCluster mjc;
+  private Path TEST_PATH = new Path("/test-dir");
+  private Path TEST_PATH_2 = new Path("/test-dir");
+
+  @Before
+  public void resetSystemExit() {
+    ExitUtil.resetFirstExitException();
+  }
+  
+  @Before
+  public void startJNs() throws Exception {
+    mjc = new MiniJournalCluster.Builder(conf).build();
+  }
+  
+  @After
+  public void stopJNs() throws Exception {
+    if (mjc != null) {
+      mjc.shutdown();
+    }
+  }
+  
+  @Test
+  public void testLogAndRestart() throws IOException {
+    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY,
+        MiniDFSCluster.getBaseDirectory() + "/TestNNWithQJM/image");
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
+        mjc.getQuorumJournalURI("myjournal").toString());
+    
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf)
+      .numDataNodes(0)
+      .manageNameDfsDirs(false)
+      .build();
+    try {
+      cluster.getFileSystem().mkdirs(TEST_PATH);
+      
+      // Restart the NN and make sure the edit was persisted
+      // and loaded again
+      cluster.restartNameNode();
+      
+      assertTrue(cluster.getFileSystem().exists(TEST_PATH));
+      cluster.getFileSystem().mkdirs(TEST_PATH_2);
+      
+      // Restart the NN again and make sure both edits are persisted.
+      cluster.restartNameNode();
+      assertTrue(cluster.getFileSystem().exists(TEST_PATH));
+      assertTrue(cluster.getFileSystem().exists(TEST_PATH_2));
+    } finally {
+      cluster.shutdown();
+    }
+  }
+  
+  @Test
+  public void testNewNamenodeTakesOverWriter() throws Exception {
+    File nn1Dir = new File(
+        MiniDFSCluster.getBaseDirectory() + "/TestNNWithQJM/image-nn1");
+    File nn2Dir = new File(
+        MiniDFSCluster.getBaseDirectory() + "/TestNNWithQJM/image-nn2");
+    
+    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY,
+        nn1Dir.getAbsolutePath());
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
+        mjc.getQuorumJournalURI("myjournal").toString());
+    
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf)
+      .numDataNodes(0)
+      .manageNameDfsDirs(false)
+      .checkExitOnShutdown(false)
+      .build();
+
+    try {
+      cluster.getFileSystem().mkdirs(TEST_PATH);
+      
+      // Start a second NN pointed to the same quorum.
+      // We need to copy the image dir from the first NN -- or else
+      // the new NN will just be rejected because of Namespace mismatch.
+      FileUtil.fullyDelete(nn2Dir);
+      FileUtil.copy(nn1Dir, FileSystem.getLocal(conf).getRaw(),
+          new Path(nn2Dir.getAbsolutePath()), false, conf);
+      
+      Configuration conf2 = new Configuration();
+      conf2.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY,
+          nn2Dir.getAbsolutePath());
+      conf2.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
+          mjc.getQuorumJournalURI("myjournal").toString());
+      MiniDFSCluster cluster2 = new MiniDFSCluster.Builder(conf2)
+        .numDataNodes(0)
+        .format(false)
+        .manageNameDfsDirs(false)
+        .build();
+      
+      // Check that the new cluster sees the edits made on the old cluster
+      try {
+        assertTrue(cluster2.getFileSystem().exists(TEST_PATH));
+      } finally {
+        cluster2.shutdown();
+      }
+      
+      // Check that, if we try to write to the old NN
+      // that it aborts.
+      try {
+        cluster.getFileSystem().mkdirs(new Path("/x"));
+        fail("Did not abort trying to write to a fenced NN");
+      } catch (RemoteException re) {
+        GenericTestUtils.assertExceptionContains(
+            "Could not sync enough journals to persistent storage", re);
+      }
+    } finally {
+      //cluster.shutdown();
+    }
+  }
+
+  @Test
+  public void testMismatchedNNIsRejected() throws Exception {
+    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY,
+        MiniDFSCluster.getBaseDirectory() + "/TestNNWithQJM/image");
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
+        mjc.getQuorumJournalURI("myjournal").toString());
+    
+    // Start a NN, so the storage is formatted -- both on-disk
+    // and QJM.
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf)
+      .numDataNodes(0)
+      .manageNameDfsDirs(false)
+      .build();
+    cluster.shutdown();
+    
+    // Reformat just the on-disk portion
+    Configuration onDiskOnly = new Configuration(conf);
+    onDiskOnly.unset(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY);
+    NameNode.format(onDiskOnly);
+
+    // Start the NN - should fail because the JNs are still formatted
+    // with the old namespace ID.
+    try {
+      cluster = new MiniDFSCluster.Builder(conf)
+        .numDataNodes(0)
+        .manageNameDfsDirs(false)
+        .format(false)
+        .build();
+      fail("New NN with different namespace should have been rejected");
+    } catch (IOException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "Unable to start log segment 1: too few journals", ioe);
+    }
+  }
+  
+  @Test
+  public void testWebPageHasQjmInfo() throws Exception {
+    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY,
+        MiniDFSCluster.getBaseDirectory() + "/TestNNWithQJM/image");
+    conf.set(DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY,
+        mjc.getQuorumJournalURI("myjournal").toString());
+    // Speed up the test
+    conf.setInt(
+        CommonConfigurationKeysPublic.IPC_CLIENT_CONNECT_MAX_RETRIES_KEY, 1);
+    
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf)
+      .numDataNodes(0)
+      .manageNameDfsDirs(false)
+      .build();
+    try {
+      URL url = new URL("http://localhost:"
+          + NameNode.getHttpAddress(cluster.getConfiguration(0)).getPort()
+          + "/dfshealth.jsp");
+      
+      cluster.getFileSystem().mkdirs(TEST_PATH);
+      
+      String contents = DFSTestUtil.urlGet(url); 
+      assertTrue(contents.contains("QJM to ["));
+      assertTrue(contents.contains("Written txid 2"));
+
+      // Stop one JN, do another txn, and make sure it shows as behind
+      // stuck behind the others.
+      mjc.getJournalNode(0).stopAndJoin(0);
+      
+      cluster.getFileSystem().delete(TEST_PATH, true);
+      
+      contents = DFSTestUtil.urlGet(url); 
+      System.out.println(contents);
+      assertTrue(Pattern.compile("1 txns/\\d+ms behind").matcher(contents)
+          .find());
+
+      // Restart NN while JN0 is still down.
+      cluster.restartNameNode();
+
+      contents = DFSTestUtil.urlGet(url); 
+      System.out.println(contents);
+      assertTrue(Pattern.compile("never written").matcher(contents)
+          .find());
+      
+
+    } finally {
+      cluster.shutdown();
+    }
+
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestEpochsAreUnique.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestEpochsAreUnique.java
new file mode 100644
index 0000000..41138d0
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestEpochsAreUnique.java
@@ -0,0 +1,144 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import static org.junit.Assert.*;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.util.Random;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.qjournal.MiniJournalCluster;
+import org.apache.hadoop.hdfs.qjournal.client.AsyncLogger;
+import org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
+
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+
+
+public class TestEpochsAreUnique {
+  private static final Log LOG = LogFactory.getLog(TestEpochsAreUnique.class);
+  private static final String JID = "testEpochsAreUnique-jid";
+  private static final NamespaceInfo FAKE_NSINFO = new NamespaceInfo(
+      12345, "mycluster", "my-bp", 0L);
+  private Random r = new Random();
+  
+  @Test
+  public void testSingleThreaded() throws IOException {
+    Configuration conf = new Configuration();
+    MiniJournalCluster cluster = new MiniJournalCluster.Builder(conf).build();
+    URI uri = cluster.getQuorumJournalURI(JID);
+    QuorumJournalManager qjm = new QuorumJournalManager(
+        conf, uri, FAKE_NSINFO);
+    try {
+      qjm.format(FAKE_NSINFO);
+    } finally {
+      qjm.close();
+    }
+    
+    try {
+      // With no failures or contention, epochs should increase one-by-one
+      for (int i = 0; i < 5; i++) {
+        qjm = new QuorumJournalManager(
+            conf, uri, FAKE_NSINFO);
+        try {
+          qjm.createNewUniqueEpoch();
+          assertEquals(i + 1, qjm.getLoggerSetForTests().getEpoch());
+        } finally {
+          qjm.close();
+        }
+      }
+      
+      long prevEpoch = 5;
+      // With some failures injected, it should still always increase, perhaps
+      // skipping some
+      for (int i = 0; i < 20; i++) {
+        long newEpoch = -1;
+        while (true) {
+          qjm = new QuorumJournalManager(
+              conf, uri, FAKE_NSINFO, new FaultyLoggerFactory());
+          try {
+            qjm.createNewUniqueEpoch();
+            newEpoch = qjm.getLoggerSetForTests().getEpoch();
+            break;
+          } catch (IOException ioe) {
+            // It's OK to fail to create an epoch, since we randomly inject
+            // faults. It's possible we'll inject faults in too many of the
+            // underlying nodes, and a failure is expected in that case
+          } finally {
+            qjm.close();
+          }
+        }
+        LOG.info("Created epoch " + newEpoch);
+        assertTrue("New epoch " + newEpoch + " should be greater than previous " +
+            prevEpoch, newEpoch > prevEpoch);
+        prevEpoch = newEpoch;
+      }
+    } finally {
+      cluster.shutdown();
+    }
+  }
+
+  private class FaultyLoggerFactory implements AsyncLogger.Factory {
+    @Override
+    public AsyncLogger createLogger(Configuration conf, NamespaceInfo nsInfo,
+        String journalId, InetSocketAddress addr) {
+      AsyncLogger ch = IPCLoggerChannel.FACTORY.createLogger(
+          conf, nsInfo, journalId, addr);
+      AsyncLogger spy = Mockito.spy(ch);
+      Mockito.doAnswer(new SometimesFaulty<Long>(0.10f))
+          .when(spy).getJournalState();
+      Mockito.doAnswer(new SometimesFaulty<Void>(0.40f))
+          .when(spy).newEpoch(Mockito.anyLong());
+
+      return spy;
+    }
+    
+  }
+
+  private class SometimesFaulty<T> implements Answer<ListenableFuture<T>> {
+    private float faultProbability;
+
+    public SometimesFaulty(float faultProbability) {
+      this.faultProbability = faultProbability;
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public ListenableFuture<T> answer(InvocationOnMock invocation)
+        throws Throwable {
+      if (r.nextFloat() < faultProbability) {
+        return Futures.immediateFailedFuture(
+            new IOException("Injected fault"));
+      }
+      return (ListenableFuture<T>)invocation.callRealMethod();
+    }
+  }
+
+
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestIPCLoggerChannel.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestIPCLoggerChannel.java
new file mode 100644
index 0000000..425bc50
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestIPCLoggerChannel.java
@@ -0,0 +1,181 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import static org.junit.Assert.*;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.qjournal.client.IPCLoggerChannel;
+import org.apache.hadoop.hdfs.qjournal.client.LoggerTooFarBehindException;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
+import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.apache.hadoop.test.GenericTestUtils.DelayAnswer;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import com.google.common.base.Supplier;
+
+public class TestIPCLoggerChannel {
+  private static final Log LOG = LogFactory.getLog(
+      TestIPCLoggerChannel.class);
+  
+  private Configuration conf = new Configuration();
+  private static final NamespaceInfo FAKE_NSINFO = new NamespaceInfo(
+      12345, "mycluster", "my-bp", 0L);
+  private static final String JID = "test-journalid";
+  private static final InetSocketAddress FAKE_ADDR =
+      new InetSocketAddress(0);
+  private static final byte[] FAKE_DATA = new byte[4096];
+  
+  private QJournalProtocol mockProxy = Mockito.mock(QJournalProtocol.class);
+  private IPCLoggerChannel ch;
+  
+  private static final int LIMIT_QUEUE_SIZE_MB = 1;
+  private static final int LIMIT_QUEUE_SIZE_BYTES =
+      LIMIT_QUEUE_SIZE_MB * 1024 * 1024;
+  
+  @Before
+  public void setupMock() {
+    conf.setInt(DFSConfigKeys.DFS_QJOURNAL_QUEUE_SIZE_LIMIT_KEY,
+        LIMIT_QUEUE_SIZE_MB);
+
+    // Channel to the mock object instead of a real IPC proxy.
+    ch = new IPCLoggerChannel(conf, FAKE_NSINFO, JID, FAKE_ADDR) {
+      @Override
+      protected QJournalProtocol getProxy() throws IOException {
+        return mockProxy;
+      }
+    };
+    
+    ch.setEpoch(1);
+  }
+  
+  @Test
+  public void testSimpleCall() throws Exception {
+    ch.sendEdits(1, 1, 3, FAKE_DATA).get();
+    Mockito.verify(mockProxy).journal(Mockito.<RequestInfo>any(),
+        Mockito.eq(1L), Mockito.eq(1L),
+        Mockito.eq(3), Mockito.same(FAKE_DATA));
+  }
+
+  
+  /**
+   * Test that, once the queue eclipses the configure size limit,
+   * calls to journal more data are rejected.
+   */
+  @Test
+  public void testQueueLimiting() throws Exception {
+    
+    // Block the underlying fake proxy from actually completing any calls.
+    DelayAnswer delayer = new DelayAnswer(LOG);
+    Mockito.doAnswer(delayer).when(mockProxy).journal(
+        Mockito.<RequestInfo>any(),
+        Mockito.eq(1L), Mockito.eq(1L),
+        Mockito.eq(1), Mockito.same(FAKE_DATA));
+    
+    // Queue up the maximum number of calls.
+    int numToQueue = LIMIT_QUEUE_SIZE_BYTES / FAKE_DATA.length;
+    for (int i = 1; i <= numToQueue; i++) {
+      ch.sendEdits(1L, (long)i, 1, FAKE_DATA);
+    }
+    
+    // The accounting should show the correct total number queued.
+    assertEquals(LIMIT_QUEUE_SIZE_BYTES, ch.getQueuedEditsSize());
+    
+    // Trying to queue any more should fail.
+    try {
+      ch.sendEdits(1L, numToQueue + 1, 1, FAKE_DATA).get(1, TimeUnit.SECONDS);
+      fail("Did not fail to queue more calls after queue was full");
+    } catch (ExecutionException ee) {
+      if (!(ee.getCause() instanceof LoggerTooFarBehindException)) {
+        throw ee;
+      }
+    }
+    
+    delayer.proceed();
+
+    // After we allow it to proceeed, it should chug through the original queue
+    GenericTestUtils.waitFor(new Supplier<Boolean>() {
+      @Override
+      public Boolean get() {
+        return ch.getQueuedEditsSize() == 0;
+      }
+    }, 10, 1000);
+  }
+  
+  /**
+   * Test that, if the remote node gets unsynchronized (eg some edits were
+   * missed or the node rebooted), the client stops sending edits until
+   * the next roll. Test for HDFS-3726.
+   */
+  @Test
+  public void testStopSendingEditsWhenOutOfSync() throws Exception {
+    Mockito.doThrow(new IOException("injected error"))
+      .when(mockProxy).journal(
+        Mockito.<RequestInfo>any(),
+        Mockito.eq(1L), Mockito.eq(1L),
+        Mockito.eq(1), Mockito.same(FAKE_DATA));
+
+    try {
+      ch.sendEdits(1L, 1L, 1, FAKE_DATA).get();
+      fail("Injected JOOSE did not cause sendEdits() to throw");
+    } catch (ExecutionException ee) {
+      GenericTestUtils.assertExceptionContains("injected", ee);
+    }
+    Mockito.verify(mockProxy).journal(
+        Mockito.<RequestInfo>any(),
+        Mockito.eq(1L), Mockito.eq(1L),
+        Mockito.eq(1), Mockito.same(FAKE_DATA));
+
+    assertTrue(ch.isOutOfSync());
+    
+    try {
+      ch.sendEdits(1L, 2L, 1, FAKE_DATA).get();
+      fail("sendEdits() should throw until next roll");
+    } catch (ExecutionException ee) {
+      GenericTestUtils.assertExceptionContains("disabled until next roll",
+          ee.getCause());
+    }
+    
+    // It should have failed without even sending the edits, since it was not sync.
+    Mockito.verify(mockProxy, Mockito.never()).journal(
+        Mockito.<RequestInfo>any(),
+        Mockito.eq(1L), Mockito.eq(2L),
+        Mockito.eq(1), Mockito.same(FAKE_DATA));
+    // It should have sent a heartbeat instead.
+    Mockito.verify(mockProxy).heartbeat(
+        Mockito.<RequestInfo>any());
+    
+    // After a roll, sending new edits should not fail.
+    ch.startLogSegment(3L).get();
+    assertFalse(ch.isOutOfSync());
+
+    ch.sendEdits(3L, 3L, 1, FAKE_DATA).get();
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQJMWithFaults.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQJMWithFaults.java
new file mode 100644
index 0000000..74daa58
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQJMWithFaults.java
@@ -0,0 +1,512 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.FAKE_NSINFO;
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.JID;
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.writeSegment;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.lang.reflect.InvocationTargetException;
+import java.net.InetSocketAddress;
+import java.net.URISyntaxException;
+import java.util.List;
+import java.util.Map;
+import java.util.Random;
+import java.util.SortedSet;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.commons.logging.impl.Log4JLogger;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
+import org.apache.hadoop.hdfs.qjournal.MiniJournalCluster;
+import org.apache.hadoop.hdfs.qjournal.QJMTestUtil;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
+import org.apache.hadoop.hdfs.qjournal.server.JournalFaultInjector;
+import org.apache.hadoop.hdfs.server.namenode.EditLogFileOutputStream;
+import org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.util.Holder;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.ipc.ProtobufRpcEngine;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.apache.log4j.Level;
+import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
+
+import com.google.common.base.Joiner;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+import com.google.common.util.concurrent.MoreExecutors;
+
+
+public class TestQJMWithFaults {
+  private static final Log LOG = LogFactory.getLog(
+      TestQJMWithFaults.class);
+
+  private static final String RAND_SEED_PROPERTY =
+      "TestQJMWithFaults.random-seed";
+
+  private static final int NUM_WRITER_ITERS = 500;
+  private static final int SEGMENTS_PER_WRITER = 2;
+
+  private static Configuration conf = new Configuration();
+
+
+  static {
+    // Don't retry connections - it just slows down the tests.
+    conf.setInt(CommonConfigurationKeysPublic.IPC_CLIENT_CONNECT_MAX_RETRIES_KEY, 0);
+    
+    // Make tests run faster by avoiding fsync()
+    EditLogFileOutputStream.setShouldSkipFsyncForTesting(true);
+  }
+
+  // Set up fault injection mock.
+  private static JournalFaultInjector faultInjector =
+      JournalFaultInjector.instance = Mockito.mock(JournalFaultInjector.class); 
+
+  /**
+   * Run through the creation of a log without any faults injected,
+   * and count how many RPCs are made to each node. This sets the
+   * bounds for the other test cases, so they can exhaustively explore
+   * the space of potential failures.
+   */
+  private static long determineMaxIpcNumber() throws Exception {
+    Configuration conf = new Configuration();
+    MiniJournalCluster cluster = new MiniJournalCluster.Builder(conf).build();
+    QuorumJournalManager qjm = null;
+    long ret;
+    try {
+      qjm = createInjectableQJM(cluster);
+      qjm.format(FAKE_NSINFO);
+      doWorkload(cluster, qjm);
+      
+      SortedSet<Integer> ipcCounts = Sets.newTreeSet();
+      for (AsyncLogger l : qjm.getLoggerSetForTests().getLoggersForTests()) {
+        InvocationCountingChannel ch = (InvocationCountingChannel)l;
+        ch.waitForAllPendingCalls();
+        ipcCounts.add(ch.getRpcCount());
+      }
+  
+      // All of the loggers should have sent the same number of RPCs, since there
+      // were no failures.
+      assertEquals(1, ipcCounts.size());
+      
+      ret = ipcCounts.first();
+      LOG.info("Max IPC count = " + ret);
+    } finally {
+      IOUtils.closeStream(qjm);
+      cluster.shutdown();
+    }
+    return ret;
+  }
+  
+  /**
+   * Sets up two of the nodes to each drop a single RPC, at all
+   * possible combinations of RPCs. This may result in the
+   * active writer failing to write. After this point, a new writer
+   * should be able to recover and continue writing without
+   * data loss.
+   */
+  @Test
+  public void testRecoverAfterDoubleFailures() throws Exception {
+    final long MAX_IPC_NUMBER = determineMaxIpcNumber();
+    
+    for (int failA = 1; failA <= MAX_IPC_NUMBER; failA++) {
+      for (int failB = 1; failB <= MAX_IPC_NUMBER; failB++) {
+        String injectionStr = "(" + failA + ", " + failB + ")";
+        
+        LOG.info("\n\n-------------------------------------------\n" +
+            "Beginning test, failing at " + injectionStr + "\n" +
+            "-------------------------------------------\n\n");
+        
+        MiniJournalCluster cluster = new MiniJournalCluster.Builder(conf)
+          .build();
+        QuorumJournalManager qjm = null;
+        try {
+          qjm = createInjectableQJM(cluster);
+          qjm.format(FAKE_NSINFO);
+          List<AsyncLogger> loggers = qjm.getLoggerSetForTests().getLoggersForTests();
+          failIpcNumber(loggers.get(0), failA);
+          failIpcNumber(loggers.get(1), failB);
+          int lastAckedTxn = doWorkload(cluster, qjm);
+
+          if (lastAckedTxn < 6) {
+            LOG.info("Failed after injecting failures at " + injectionStr + 
+                ". This is expected since we injected a failure in the " +
+                "majority.");
+          }
+          qjm.close();
+          qjm = null;
+
+          // Now should be able to recover
+          qjm = createInjectableQJM(cluster);
+          long lastRecoveredTxn = QJMTestUtil.recoverAndReturnLastTxn(qjm);
+          assertTrue(lastRecoveredTxn >= lastAckedTxn);
+          
+          writeSegment(cluster, qjm, lastRecoveredTxn + 1, 3, true);
+        } catch (Throwable t) {
+          // Test failure! Rethrow with the test setup info so it can be
+          // easily triaged.
+          throw new RuntimeException("Test failed with injection: " + injectionStr,
+                t); 
+        } finally {
+          cluster.shutdown();
+          cluster = null;
+          IOUtils.closeStream(qjm);
+          qjm = null;
+        }
+      }
+    }
+  }
+  
+  /**
+   * Test case in which three JournalNodes randomly flip flop between
+   * up and down states every time they get an RPC.
+   * 
+   * The writer keeps track of the latest ACKed edit, and on every
+   * recovery operation, ensures that it recovers at least to that
+   * point or higher. Since at any given point, a majority of JNs
+   * may be injecting faults, any writer operation is allowed to fail,
+   * so long as the exception message indicates it failed due to injected
+   * faults.
+   * 
+   * Given a random seed, the test should be entirely deterministic.
+   */
+  @Test
+  public void testRandomized() throws Exception {
+    long seed;
+    Long userSpecifiedSeed = Long.getLong(RAND_SEED_PROPERTY);
+    if (userSpecifiedSeed != null) {
+      LOG.info("Using seed specified in system property");
+      seed = userSpecifiedSeed;
+      
+      // If the user specifies a seed, then we should gather all the
+      // IPC trace information so that debugging is easier. This makes
+      // the test run about 25% slower otherwise.
+      ((Log4JLogger)ProtobufRpcEngine.LOG).getLogger().setLevel(Level.ALL);
+    } else {
+      seed = new Random().nextLong();
+    }
+    LOG.info("Random seed: " + seed);
+    
+    Random r = new Random(seed);
+    
+    MiniJournalCluster cluster = new MiniJournalCluster.Builder(conf)
+      .build();
+    
+    // Format the cluster using a non-faulty QJM.
+    QuorumJournalManager qjmForInitialFormat =
+        createInjectableQJM(cluster);
+    qjmForInitialFormat.format(FAKE_NSINFO);
+    qjmForInitialFormat.close();
+    
+    try {
+      long txid = 0;
+      long lastAcked = 0;
+      
+      for (int i = 0; i < NUM_WRITER_ITERS; i++) {
+        LOG.info("Starting writer " + i + "\n-------------------");
+        
+        QuorumJournalManager qjm = createRandomFaultyQJM(cluster, r);
+        try {
+          long recovered;
+          try {
+            recovered = QJMTestUtil.recoverAndReturnLastTxn(qjm);
+          } catch (Throwable t) {
+            LOG.info("Failed recovery", t);
+            checkException(t);
+            continue;
+          }
+          assertTrue("Recovered only up to txnid " + recovered +
+              " but had gotten an ack for " + lastAcked,
+              recovered >= lastAcked);
+          
+          txid = recovered + 1;
+          
+          // Periodically purge old data on disk so it's easier to look
+          // at failure cases.
+          if (txid > 100 && i % 10 == 1) {
+            qjm.purgeLogsOlderThan(txid - 100);
+          }
+
+          Holder<Throwable> thrown = new Holder<Throwable>(null);
+          for (int j = 0; j < SEGMENTS_PER_WRITER; j++) {
+            lastAcked = writeSegmentUntilCrash(cluster, qjm, txid, 4, thrown);
+            if (thrown.held != null) {
+              LOG.info("Failed write", thrown.held);
+              checkException(thrown.held);
+              break;
+            }
+            txid += 4;
+          }
+        } finally {
+          qjm.close();
+        }
+      }
+    } finally {
+      cluster.shutdown();
+    }
+  }
+
+  private void checkException(Throwable t) {
+    GenericTestUtils.assertExceptionContains("Injected", t);
+    if (t.toString().contains("AssertionError")) {
+      throw new RuntimeException("Should never see AssertionError in fault test!",
+          t);
+    }
+  }
+
+  private long writeSegmentUntilCrash(MiniJournalCluster cluster,
+      QuorumJournalManager qjm, long txid, int numTxns, Holder<Throwable> thrown) {
+    
+    long firstTxId = txid;
+    long lastAcked = txid - 1;
+    try {
+      EditLogOutputStream stm = qjm.startLogSegment(txid);
+      
+      for (int i = 0; i < numTxns; i++) {
+        QJMTestUtil.writeTxns(stm, txid++, 1);
+        lastAcked++;
+      }
+      
+      stm.close();
+      qjm.finalizeLogSegment(firstTxId, lastAcked);
+    } catch (Throwable t) {
+      thrown.held = t;
+    }
+    return lastAcked;
+  }
+
+  /**
+   * Run a simple workload of becoming the active writer and writing
+   * two log segments: 1-3 and 4-6.
+   */
+  private static int doWorkload(MiniJournalCluster cluster,
+      QuorumJournalManager qjm) throws IOException {
+    int lastAcked = 0;
+    try {
+      qjm.recoverUnfinalizedSegments();
+      writeSegment(cluster, qjm, 1, 3, true);
+      lastAcked = 3;
+      writeSegment(cluster, qjm, 4, 3, true);
+      lastAcked = 6;
+    } catch (QuorumException qe) {
+      LOG.info("Failed to write at txid " + lastAcked,
+          qe);
+    }
+    return lastAcked;
+  }
+
+  /**
+   * Inject a failure at the given IPC number, such that the JN never
+   * receives the RPC. The client side sees an IOException. Future
+   * IPCs after this number will be received as usual.
+   */
+  private void failIpcNumber(AsyncLogger logger, int idx) {
+    ((InvocationCountingChannel)logger).failIpcNumber(idx);
+  }
+  
+  private static class RandomFaultyChannel extends IPCLoggerChannel {
+    private final Random random;
+    private float injectionProbability = 0.1f;
+    private boolean isUp = true;
+    
+    public RandomFaultyChannel(Configuration conf, NamespaceInfo nsInfo,
+        String journalId, InetSocketAddress addr, long seed) {
+      super(conf, nsInfo, journalId, addr);
+      this.random = new Random(seed);
+    }
+
+    @Override
+    protected QJournalProtocol createProxy() throws IOException {
+      QJournalProtocol realProxy = super.createProxy();
+      return mockProxy(
+          new WrapEveryCall<Object>(realProxy) {
+            @Override
+            void beforeCall(InvocationOnMock invocation) throws Exception {
+              if (random.nextFloat() < injectionProbability) {
+                isUp = !isUp;
+                LOG.info("transitioned " + addr + " to " +
+                    (isUp ? "up" : "down"));
+              }
+    
+              if (!isUp) {
+                throw new IOException("Injected - faking being down");
+              }
+              
+              if (invocation.getMethod().getName().equals("acceptRecovery")) {
+                if (random.nextFloat() < injectionProbability) {
+                  Mockito.doThrow(new IOException(
+                      "Injected - faking fault before persisting paxos data"))
+                      .when(faultInjector).beforePersistPaxosData();
+                } else if (random.nextFloat() < injectionProbability) {
+                  Mockito.doThrow(new IOException(
+                      "Injected - faking fault after persisting paxos data"))
+                      .when(faultInjector).afterPersistPaxosData();
+                }
+              }
+            }
+            
+            @Override
+            public void afterCall(InvocationOnMock invocation, boolean succeeded) {
+              Mockito.reset(faultInjector);
+            }
+          });
+    }
+
+    @Override
+    protected ExecutorService createExecutor() {
+      return MoreExecutors.sameThreadExecutor();
+    }
+  }
+
+  private static class InvocationCountingChannel extends IPCLoggerChannel {
+    private int rpcCount = 0;
+    private Map<Integer, Callable<Void>> injections = Maps.newHashMap();
+    
+    public InvocationCountingChannel(Configuration conf, NamespaceInfo nsInfo,
+        String journalId, InetSocketAddress addr) {
+      super(conf, nsInfo, journalId, addr);
+    }
+    
+    int getRpcCount() {
+      return rpcCount;
+    }
+    
+    void failIpcNumber(final int idx) {
+      Preconditions.checkArgument(idx > 0,
+          "id must be positive");
+      inject(idx, new Callable<Void>() {
+        @Override
+        public Void call() throws Exception {
+          throw new IOException("injected failed IPC at " + idx);
+        }
+      });
+    }
+    
+    private void inject(int beforeRpcNumber, Callable<Void> injectedCode) {
+      injections.put(beforeRpcNumber, injectedCode);
+    }
+
+    @Override
+    protected QJournalProtocol createProxy() throws IOException {
+      final QJournalProtocol realProxy = super.createProxy();
+      QJournalProtocol mock = mockProxy(
+          new WrapEveryCall<Object>(realProxy) {
+            void beforeCall(InvocationOnMock invocation) throws Exception {
+              rpcCount++;
+              String callStr = "[" + addr + "] " + 
+                  invocation.getMethod().getName() + "(" +
+                  Joiner.on(", ").join(invocation.getArguments()) + ")";
+ 
+              Callable<Void> inject = injections.get(rpcCount);
+              if (inject != null) {
+                LOG.info("Injecting code before IPC #" + rpcCount + ": " +
+                    callStr);
+                inject.call();
+              } else {
+                LOG.info("IPC call #" + rpcCount + ": " + callStr);
+              }
+            }
+          });
+      return mock;
+    }
+  }
+
+
+  private static QJournalProtocol mockProxy(WrapEveryCall<Object> wrapper)
+      throws IOException {
+    QJournalProtocol mock = Mockito.mock(QJournalProtocol.class,
+        Mockito.withSettings()
+          .defaultAnswer(wrapper)
+          .extraInterfaces(Closeable.class));
+    return mock;
+  }
+
+  private static abstract class WrapEveryCall<T> implements Answer<T> {
+    private final Object realObj;
+    WrapEveryCall(Object realObj) {
+      this.realObj = realObj;
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public T answer(InvocationOnMock invocation) throws Throwable {
+      // Don't want to inject an error on close() since that isn't
+      // actually an IPC call!
+      if (!Closeable.class.equals(
+            invocation.getMethod().getDeclaringClass())) {
+        beforeCall(invocation);
+      }
+      boolean success = false;
+      try {
+        T ret = (T) invocation.getMethod().invoke(realObj,
+          invocation.getArguments());
+        success = true;
+        return ret;
+      } catch (InvocationTargetException ite) {
+        throw ite.getCause();
+      } finally {
+        afterCall(invocation, success);
+      }
+    }
+
+    abstract void beforeCall(InvocationOnMock invocation) throws Exception;
+    void afterCall(InvocationOnMock invocation, boolean succeeded) {}
+  }
+  
+  private static QuorumJournalManager createInjectableQJM(MiniJournalCluster cluster)
+      throws IOException, URISyntaxException {
+    AsyncLogger.Factory spyFactory = new AsyncLogger.Factory() {
+      @Override
+      public AsyncLogger createLogger(Configuration conf, NamespaceInfo nsInfo,
+          String journalId, InetSocketAddress addr) {
+        return new InvocationCountingChannel(conf, nsInfo, journalId, addr);
+      }
+    };
+    return new QuorumJournalManager(conf, cluster.getQuorumJournalURI(JID),
+        FAKE_NSINFO, spyFactory);
+  }
+  
+  private static QuorumJournalManager createRandomFaultyQJM(
+      MiniJournalCluster cluster, final Random seedGenerator)
+          throws IOException, URISyntaxException {
+    
+    AsyncLogger.Factory spyFactory = new AsyncLogger.Factory() {
+      @Override
+      public AsyncLogger createLogger(Configuration conf, NamespaceInfo nsInfo,
+          String journalId, InetSocketAddress addr) {
+        return new RandomFaultyChannel(conf, nsInfo, journalId, addr,
+            seedGenerator.nextLong());
+      }
+    };
+    return new QuorumJournalManager(conf, cluster.getQuorumJournalURI(JID),
+        FAKE_NSINFO, spyFactory);
+  }
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumCall.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumCall.java
new file mode 100644
index 0000000..2295384
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumCall.java
@@ -0,0 +1,69 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import static org.junit.Assert.*;
+
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.concurrent.TimeoutException;
+
+import org.apache.hadoop.hdfs.qjournal.client.QuorumCall;
+import org.junit.Test;
+
+import com.google.common.base.Joiner;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.util.concurrent.SettableFuture;
+
+public class TestQuorumCall {
+  @Test(timeout=10000)
+  public void testQuorums() throws Exception {
+    Map<String, SettableFuture<String>> futures = ImmutableMap.of(
+        "f1", SettableFuture.<String>create(),
+        "f2", SettableFuture.<String>create(),
+        "f3", SettableFuture.<String>create());
+    
+    QuorumCall<String, String> q = QuorumCall.create(futures);
+    assertEquals(0, q.countResponses());
+    
+    futures.get("f1").set("first future");
+    q.waitFor(1, 0, 0, 100000, "test"); // wait for 1 response
+    q.waitFor(0, 1, 0, 100000, "test"); // wait for 1 success
+    assertEquals(1, q.countResponses());
+    
+    
+    futures.get("f2").setException(new Exception("error"));
+    assertEquals(2, q.countResponses());
+    
+    futures.get("f3").set("second future");
+    q.waitFor(3, 0, 100, 100000, "test"); // wait for 3 responses
+    q.waitFor(0, 2, 100, 100000, "test"); // 2 successes
+
+    assertEquals(3, q.countResponses());
+    assertEquals("f1=first future,f3=second future",
+        Joiner.on(",").withKeyValueSeparator("=").join(
+            new TreeMap<String, String>(q.getResults())));
+    
+    try {
+      q.waitFor(0, 4, 100, 10, "test");
+      fail("Didn't time out waiting for more responses than came back");
+    } catch (TimeoutException te) {
+      // expected
+    }
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumJournalManager.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumJournalManager.java
new file mode 100644
index 0000000..7c2bb29
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumJournalManager.java
@@ -0,0 +1,941 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import static org.junit.Assert.*;
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.JID;
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.FAKE_NSINFO;
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.writeSegment;
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.writeTxns;
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.verifyEdits;
+import static org.apache.hadoop.hdfs.qjournal.client.TestQuorumJournalManagerUnit.futureThrows;
+
+import java.io.Closeable;
+import java.io.File;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.commons.logging.impl.Log4JLogger;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
+import org.apache.hadoop.hdfs.qjournal.MiniJournalCluster;
+import org.apache.hadoop.hdfs.qjournal.QJMTestUtil;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.apache.hadoop.hdfs.qjournal.server.JournalFaultInjector;
+import org.apache.hadoop.hdfs.server.namenode.EditLogInputStream;
+import org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream;
+import org.apache.hadoop.hdfs.server.namenode.FileJournalManager;
+import org.apache.hadoop.hdfs.server.namenode.FileJournalManager.EditLogFile;
+import org.apache.hadoop.hdfs.server.namenode.NNStorage;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.ipc.ProtobufRpcEngine;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.apache.log4j.Level;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.stubbing.Stubber;
+
+import com.google.common.collect.Lists;
+import com.google.common.util.concurrent.MoreExecutors;
+
+/**
+ * Functional tests for QuorumJournalManager.
+ * For true unit tests, see {@link TestQuorumJournalManagerUnit}.
+ */
+public class TestQuorumJournalManager {
+  private static final Log LOG = LogFactory.getLog(
+      TestQuorumJournalManager.class);
+  
+  private MiniJournalCluster cluster;
+  private Configuration conf;
+  private QuorumJournalManager qjm;
+  private List<AsyncLogger> spies;
+  
+  static {
+    ((Log4JLogger)ProtobufRpcEngine.LOG).getLogger().setLevel(Level.ALL);
+  }
+
+  @Before
+  public void setup() throws Exception {
+    conf = new Configuration();
+    // Don't retry connections - it just slows down the tests.
+    conf.setInt(CommonConfigurationKeysPublic.IPC_CLIENT_CONNECT_MAX_RETRIES_KEY, 0);
+    
+    cluster = new MiniJournalCluster.Builder(conf)
+      .build();
+    
+    qjm = createSpyingQJM();
+    spies = qjm.getLoggerSetForTests().getLoggersForTests();
+
+    qjm.format(QJMTestUtil.FAKE_NSINFO);
+    qjm.recoverUnfinalizedSegments();
+    assertEquals(1, qjm.getLoggerSetForTests().getEpoch());
+  }
+  
+  @After
+  public void shutdown() throws IOException {
+    if (cluster != null) {
+      cluster.shutdown();
+    }
+  }
+  
+  @Test
+  public void testSingleWriter() throws Exception {
+    writeSegment(cluster, qjm, 1, 3, true);
+    
+    // Should be finalized
+    checkRecovery(cluster, 1, 3);
+    
+    // Start a new segment
+    writeSegment(cluster, qjm, 4, 1, true);
+
+    // Should be finalized
+    checkRecovery(cluster, 4, 4);
+  }
+  
+  @Test
+  public void testFormat() throws Exception {
+    QuorumJournalManager qjm = new QuorumJournalManager(
+        conf, cluster.getQuorumJournalURI("testFormat-jid"), FAKE_NSINFO);
+    assertFalse(qjm.hasSomeData());
+    qjm.format(FAKE_NSINFO);
+    assertTrue(qjm.hasSomeData());
+  }
+  
+  @Test
+  public void testReaderWhileAnotherWrites() throws Exception {
+    
+    QuorumJournalManager readerQjm = createSpyingQJM();
+    List<EditLogInputStream> streams = Lists.newArrayList();
+    readerQjm.selectInputStreams(streams, 0, false);
+    assertEquals(0, streams.size());
+    writeSegment(cluster, qjm, 1, 3, true);
+
+    readerQjm.selectInputStreams(streams, 0, false);
+    try {
+      assertEquals(1, streams.size());
+      // Validate the actual stream contents.
+      EditLogInputStream stream = streams.get(0);
+      assertEquals(1, stream.getFirstTxId());
+      assertEquals(3, stream.getLastTxId());
+      
+      verifyEdits(streams, 1, 3);
+      assertNull(stream.readOp());
+    } finally {
+      IOUtils.cleanup(LOG, streams.toArray(new Closeable[0]));
+      streams.clear();
+    }
+    
+    // Ensure correct results when there is a stream in-progress, but we don't
+    // ask for in-progress.
+    writeSegment(cluster, qjm, 4, 3, false);
+    readerQjm.selectInputStreams(streams, 0, false);
+    try {
+      assertEquals(1, streams.size());
+      EditLogInputStream stream = streams.get(0);
+      assertEquals(1, stream.getFirstTxId());
+      assertEquals(3, stream.getLastTxId());
+      verifyEdits(streams, 1, 3);
+    } finally {
+      IOUtils.cleanup(LOG, streams.toArray(new Closeable[0]));
+      streams.clear();
+    }
+    
+    // TODO: check results for selectInputStreams with inProgressOK = true.
+    // This doesn't currently work, due to a bug where RedundantEditInputStream
+    // throws an exception if there are any unvalidated in-progress edits in the list!
+    // But, it shouldn't be necessary for current use cases.
+    
+    qjm.finalizeLogSegment(4, 6);
+    readerQjm.selectInputStreams(streams, 0, false);
+    try {
+      assertEquals(2, streams.size());
+      assertEquals(4, streams.get(1).getFirstTxId());
+      assertEquals(6, streams.get(1).getLastTxId());
+
+      verifyEdits(streams, 1, 6);
+    } finally {
+      IOUtils.cleanup(LOG, streams.toArray(new Closeable[0]));
+      streams.clear();
+    }
+  }
+  
+  /**
+   * Regression test for HDFS-3725. One of the journal nodes is down
+   * during the writing of one segment, then comes back up later to
+   * take part in a later segment. Thus, its local edits are
+   * not a contiguous sequence. This should be handled correctly.
+   */
+  @Test
+  public void testOneJNMissingSegments() throws Exception {
+    writeSegment(cluster, qjm, 1, 3, true);
+    waitForAllPendingCalls(qjm.getLoggerSetForTests());
+    cluster.getJournalNode(0).stopAndJoin(0);
+    writeSegment(cluster, qjm, 4, 3, true);
+    waitForAllPendingCalls(qjm.getLoggerSetForTests());
+    cluster.restartJournalNode(0);
+    writeSegment(cluster, qjm, 7, 3, true);
+    waitForAllPendingCalls(qjm.getLoggerSetForTests());
+    cluster.getJournalNode(1).stopAndJoin(0);
+    
+    QuorumJournalManager readerQjm = createSpyingQJM();
+    List<EditLogInputStream> streams = Lists.newArrayList();
+    try {
+      readerQjm.selectInputStreams(streams, 1, false);
+      verifyEdits(streams, 1, 9);
+    } finally {
+      IOUtils.cleanup(LOG, streams.toArray(new Closeable[0]));
+      readerQjm.close();
+    }
+  }
+  
+  /**
+   * Regression test for HDFS-3891: selectInputStreams should throw
+   * an exception when a majority of journalnodes have crashed.
+   */
+  @Test
+  public void testSelectInputStreamsMajorityDown() throws Exception {
+    // Shut down all of the JNs.
+    cluster.shutdown();
+
+    List<EditLogInputStream> streams = Lists.newArrayList();
+    try {
+      qjm.selectInputStreams(streams, 0, false);
+      fail("Did not throw IOE");
+    } catch (QuorumException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "Got too many exceptions", ioe);
+      assertTrue(streams.isEmpty());
+    }
+  }
+  
+  /**
+   * Test the case where the NN crashes after starting a new segment
+   * on all nodes, but before writing the first transaction to it.
+   */
+  @Test
+  public void testCrashAtBeginningOfSegment() throws Exception {
+    writeSegment(cluster, qjm, 1, 3, true);
+    waitForAllPendingCalls(qjm.getLoggerSetForTests());
+    
+    EditLogOutputStream stm = qjm.startLogSegment(4);
+    try {
+      waitForAllPendingCalls(qjm.getLoggerSetForTests());
+    } finally {
+      stm.abort();
+    }
+    
+    
+    // Make a new QJM
+    qjm = new QuorumJournalManager(
+        conf, cluster.getQuorumJournalURI(JID), FAKE_NSINFO);
+    qjm.recoverUnfinalizedSegments();
+    checkRecovery(cluster, 1, 3);
+
+    writeSegment(cluster, qjm, 4, 3, true);
+  }
+  
+  @Test
+  public void testOutOfSyncAtBeginningOfSegment0() throws Exception {
+    doTestOutOfSyncAtBeginningOfSegment(0);
+  }
+  
+  @Test
+  public void testOutOfSyncAtBeginningOfSegment1() throws Exception {
+    doTestOutOfSyncAtBeginningOfSegment(1);
+  }
+
+  @Test
+  public void testOutOfSyncAtBeginningOfSegment2() throws Exception {
+    doTestOutOfSyncAtBeginningOfSegment(2);
+  }
+  
+  /**
+   * Test the case where, at the beginning of a segment, transactions
+   * have been written to one JN but not others.
+   */
+  public void doTestOutOfSyncAtBeginningOfSegment(int nodeWithOneTxn)
+      throws Exception {
+    
+    int nodeWithEmptySegment = (nodeWithOneTxn + 1) % 3;
+    int nodeMissingSegment = (nodeWithOneTxn + 2) % 3;
+    
+    writeSegment(cluster, qjm, 1, 3, true);
+    waitForAllPendingCalls(qjm.getLoggerSetForTests());
+    cluster.getJournalNode(nodeMissingSegment).stopAndJoin(0);
+    
+    // Open segment on 2/3 nodes
+    EditLogOutputStream stm = qjm.startLogSegment(4);
+    try {
+      waitForAllPendingCalls(qjm.getLoggerSetForTests());
+      
+      // Write transactions to only 1/3 nodes
+      failLoggerAtTxn(spies.get(nodeWithEmptySegment), 4);
+      try {
+        writeTxns(stm, 4, 1);
+        fail("Did not fail even though 2/3 failed");
+      } catch (QuorumException qe) {
+        GenericTestUtils.assertExceptionContains("mock failure", qe);
+      }
+    } finally {
+      stm.abort();
+    }
+    
+    // Bring back the down JN.
+    cluster.restartJournalNode(nodeMissingSegment);
+    
+    // Make a new QJM. At this point, the state is as follows:
+    // A: nodeWithEmptySegment: 1-3 finalized, 4_inprogress (empty)    
+    // B: nodeWithOneTxn:       1-3 finalized, 4_inprogress (1 txn)
+    // C: nodeMissingSegment:   1-3 finalized
+    GenericTestUtils.assertGlobEquals(
+        cluster.getCurrentDir(nodeWithEmptySegment, JID),
+        "edits_.*",
+        NNStorage.getFinalizedEditsFileName(1, 3),
+        NNStorage.getInProgressEditsFileName(4));
+    GenericTestUtils.assertGlobEquals(
+        cluster.getCurrentDir(nodeWithOneTxn, JID),
+        "edits_.*",
+        NNStorage.getFinalizedEditsFileName(1, 3),
+        NNStorage.getInProgressEditsFileName(4));
+    GenericTestUtils.assertGlobEquals(
+        cluster.getCurrentDir(nodeMissingSegment, JID),
+        "edits_.*",
+        NNStorage.getFinalizedEditsFileName(1, 3));
+    
+
+    // Stop one of the nodes. Since we run this test three
+    // times, rotating the roles of the nodes, we'll test
+    // all the permutations.
+    cluster.getJournalNode(2).stopAndJoin(0);
+  
+    qjm = createSpyingQJM();
+    qjm.recoverUnfinalizedSegments();
+    
+    if (nodeWithOneTxn == 0 ||
+        nodeWithOneTxn == 1) {
+      // If the node that had the transaction committed was one of the nodes
+      // that responded during recovery, then we should have recovered txid
+      // 4.
+      checkRecovery(cluster, 4, 4);
+      writeSegment(cluster, qjm, 5, 3, true);
+    } else {
+      // Otherwise, we should have recovered only 1-3 and should be able to
+      // start a segment at 4.
+      checkRecovery(cluster, 1, 3);
+      writeSegment(cluster, qjm, 4, 3, true);
+    }
+  }
+
+  
+  /**
+   * Test case where a new writer picks up from an old one with no failures
+   * and the previous unfinalized segment entirely consistent -- i.e. all
+   * the JournalNodes end at the same transaction ID.
+   */
+  @Test
+  public void testChangeWritersLogsInSync() throws Exception {
+    writeSegment(cluster, qjm, 1, 3, false);
+    QJMTestUtil.assertExistsInQuorum(cluster,
+        NNStorage.getInProgressEditsFileName(1));
+
+    // Make a new QJM
+    qjm = new QuorumJournalManager(
+        conf, cluster.getQuorumJournalURI(JID), FAKE_NSINFO);
+    qjm.recoverUnfinalizedSegments();
+    checkRecovery(cluster, 1, 3);
+  }
+  
+  /**
+   * Test case where a new writer picks up from an old one which crashed
+   * with the three loggers at different txnids
+   */
+  @Test
+  public void testChangeWritersLogsOutOfSync1() throws Exception {
+    // Journal states:  [3, 4, 5]
+    // During recovery: [x, 4, 5]
+    // Should recovery to txn 5
+    doOutOfSyncTest(0, 5L);
+  }
+
+  @Test
+  public void testChangeWritersLogsOutOfSync2() throws Exception {
+    // Journal states:  [3, 4, 5]
+    // During recovery: [3, x, 5]
+    // Should recovery to txn 5
+    doOutOfSyncTest(1, 5L);
+  }
+
+  @Test
+  public void testChangeWritersLogsOutOfSync3() throws Exception {
+    // Journal states:  [3, 4, 5]
+    // During recovery: [3, 4, x]
+    // Should recovery to txn 4
+    doOutOfSyncTest(2, 4L);
+  }
+
+  
+  private void doOutOfSyncTest(int missingOnRecoveryIdx,
+      long expectedRecoveryTxnId) throws Exception {
+    setupLoggers345();
+    
+    QJMTestUtil.assertExistsInQuorum(cluster,
+        NNStorage.getInProgressEditsFileName(1));
+
+    // Shut down the specified JN, so it's not present during recovery.
+    cluster.getJournalNode(missingOnRecoveryIdx).stopAndJoin(0);
+
+    // Make a new QJM
+    qjm = createSpyingQJM();
+    
+    qjm.recoverUnfinalizedSegments();
+    checkRecovery(cluster, 1, expectedRecoveryTxnId);
+  }
+  
+  
+  private void failLoggerAtTxn(AsyncLogger spy, long txid) {
+    TestQuorumJournalManagerUnit.futureThrows(new IOException("mock failure"))
+      .when(spy).sendEdits(Mockito.anyLong(),
+        Mockito.eq(txid), Mockito.eq(1), Mockito.<byte[]>any());
+  }
+  
+  /**
+   * Test the case where one of the loggers misses a finalizeLogSegment()
+   * call, and then misses the next startLogSegment() call before coming
+   * back to life.
+   * 
+   * Previously, this caused it to keep on writing to the old log segment,
+   * such that one logger had eg edits_1-10 while the others had edits_1-5 and
+   * edits_6-10. This caused recovery to fail in certain cases.
+   */
+  @Test
+  public void testMissFinalizeAndNextStart() throws Exception {
+    
+    // Logger 0: miss finalize(1-3) and start(4)
+    futureThrows(new IOException("injected")).when(spies.get(0))
+      .finalizeLogSegment(Mockito.eq(1L), Mockito.eq(3L));
+    futureThrows(new IOException("injected")).when(spies.get(0))
+      .startLogSegment(Mockito.eq(4L));
+    
+    // Logger 1: fail at txn id 4
+    failLoggerAtTxn(spies.get(1), 4L);
+    
+    writeSegment(cluster, qjm, 1, 3, true);
+    EditLogOutputStream stm = qjm.startLogSegment(4);
+    try {
+      writeTxns(stm, 4, 1);
+      fail("Did not fail to write");
+    } catch (QuorumException qe) {
+      // Should fail, because logger 1 had an injected fault and
+      // logger 0 should detect writer out of sync
+      GenericTestUtils.assertExceptionContains("Writer out of sync",
+          qe);
+    } finally {
+      stm.abort();
+      qjm.close();
+    }
+    
+    // State:
+    // Logger 0: 1-3 in-progress (since it missed finalize)
+    // Logger 1: 1-3 finalized
+    // Logger 2: 1-3 finalized, 4 in-progress with one txn
+    
+    // Shut down logger 2 so it doesn't participate in recovery
+    cluster.getJournalNode(2).stopAndJoin(0);
+    
+    qjm = createSpyingQJM();
+    long recovered = QJMTestUtil.recoverAndReturnLastTxn(qjm);
+    assertEquals(3L, recovered);
+  }
+  
+  /**
+   * edit lengths [3,4,5]
+   * first recovery:
+   * - sees [3,4,x]
+   * - picks length 4 for recoveryEndTxId
+   * - calls acceptRecovery()
+   * - crashes before finalizing
+   * second recovery:
+   * - sees [x, 4, 5]
+   * - should pick recovery length 4, even though it saw
+   *   a larger txid, because a previous recovery accepted it
+   */
+  @Test
+  public void testRecoverAfterIncompleteRecovery() throws Exception {
+    setupLoggers345();
+
+    // Shut down the logger that has length = 5
+    cluster.getJournalNode(2).stopAndJoin(0);
+
+    qjm = createSpyingQJM();
+    spies = qjm.getLoggerSetForTests().getLoggersForTests();
+
+    // Allow no logger to finalize
+    for (AsyncLogger spy : spies) {
+      TestQuorumJournalManagerUnit.futureThrows(new IOException("injected"))
+        .when(spy).finalizeLogSegment(Mockito.eq(1L),
+            Mockito.eq(4L));
+    }
+    try {
+      qjm.recoverUnfinalizedSegments();
+      fail("Should have failed recovery since no finalization occurred");
+    } catch (IOException ioe) {
+      GenericTestUtils.assertExceptionContains("injected", ioe);
+    }
+    
+    // Now bring back the logger that had 5, and run recovery again.
+    // We should recover to 4, even though there's a longer log.
+    cluster.getJournalNode(0).stopAndJoin(0);
+    cluster.restartJournalNode(2);
+    
+    qjm = createSpyingQJM();
+    spies = qjm.getLoggerSetForTests().getLoggersForTests();
+    qjm.recoverUnfinalizedSegments();
+    checkRecovery(cluster, 1, 4);
+  }
+  
+  /**
+   * Set up the loggers into the following state:
+   * - JN0: edits 1-3 in progress
+   * - JN1: edits 1-4 in progress
+   * - JN2: edits 1-5 in progress
+   * 
+   * None of the loggers have any associated paxos info.
+   */
+  private void setupLoggers345() throws Exception {
+    EditLogOutputStream stm = qjm.startLogSegment(1);
+    
+    failLoggerAtTxn(spies.get(0), 4);
+    failLoggerAtTxn(spies.get(1), 5);
+    
+    writeTxns(stm, 1, 3);
+    
+    // This should succeed to 2/3 loggers
+    writeTxns(stm, 4, 1);
+    
+    // This should only succeed to 1 logger (index 2). Hence it should
+    // fail
+    try {
+      writeTxns(stm, 5, 1);
+      fail("Did not fail to write when only a minority succeeded");
+    } catch (QuorumException qe) {
+      GenericTestUtils.assertExceptionContains(
+          "too many exceptions to achieve quorum size 2/3",
+          qe);
+    }
+  }
+
+  /**
+   * Set up the following tricky edge case state which is used by
+   * multiple tests:
+   * 
+   * Initial writer:
+   * - Writing to 3 JNs: JN0, JN1, JN2:
+   * - A log segment with txnid 1 through 100 succeeds.
+   * - The first transaction in the next segment only goes to JN0
+   *   before the writer crashes (eg it is partitioned)
+   *   
+   * Recovery by another writer:
+   * - The new NN starts recovery and talks to all three. Thus, it sees
+   *   that the newest log segment which needs recovery is 101.
+   * - It sends the prepareRecovery(101) call, and decides that the
+   *   recovery length for 101 is only the 1 transaction.
+   * - It sends acceptRecovery(101-101) to only JN0, before crashing
+   * 
+   * This yields the following state:
+   * - JN0: 1-100 finalized, 101_inprogress, accepted recovery: 101-101
+   * - JN1: 1-100 finalized, 101_inprogress.empty
+   * - JN2: 1-100 finalized, 101_inprogress.empty
+   *  (the .empty files got moved aside during recovery)
+   * @throws Exception 
+   */
+  private void setupEdgeCaseOneJnHasSegmentWithAcceptedRecovery() throws Exception {
+    // Log segment with txns 1-100 succeeds 
+    writeSegment(cluster, qjm, 1, 100, true);
+
+    // startLogSegment only makes it to one of the three nodes
+    failLoggerAtTxn(spies.get(1), 101);
+    failLoggerAtTxn(spies.get(2), 101);
+    
+    try {
+      writeSegment(cluster, qjm, 101, 1, true);
+      fail("Should have failed");
+    } catch (QuorumException qe) {
+      GenericTestUtils.assertExceptionContains("mock failure", qe);
+    } finally {
+      qjm.close();
+    }
+    
+    // Recovery 1:
+    // make acceptRecovery() only make it to the node which has txid 101
+    // this should fail because only 1/3 accepted the recovery
+    qjm = createSpyingQJM();
+    spies = qjm.getLoggerSetForTests().getLoggersForTests();
+    futureThrows(new IOException("mock failure")).when(spies.get(1))
+      .acceptRecovery(Mockito.<SegmentStateProto>any(), Mockito.<URL>any());
+    futureThrows(new IOException("mock failure")).when(spies.get(2))
+      .acceptRecovery(Mockito.<SegmentStateProto>any(), Mockito.<URL>any());
+    
+    try {
+      qjm.recoverUnfinalizedSegments();
+      fail("Should have failed to recover");
+    } catch (QuorumException qe) {
+      GenericTestUtils.assertExceptionContains("mock failure", qe);
+    } finally {
+      qjm.close();
+    }
+    
+    // Check that we have entered the expected state as described in the
+    // method javadoc.
+    GenericTestUtils.assertGlobEquals(cluster.getCurrentDir(0, JID),
+        "edits_.*",
+        NNStorage.getFinalizedEditsFileName(1, 100),
+        NNStorage.getInProgressEditsFileName(101));
+    GenericTestUtils.assertGlobEquals(cluster.getCurrentDir(1, JID),
+        "edits_.*",
+        NNStorage.getFinalizedEditsFileName(1, 100),
+        NNStorage.getInProgressEditsFileName(101) + ".empty");
+    GenericTestUtils.assertGlobEquals(cluster.getCurrentDir(2, JID),
+        "edits_.*",
+        NNStorage.getFinalizedEditsFileName(1, 100),
+        NNStorage.getInProgressEditsFileName(101) + ".empty");
+
+    File paxos0 = new File(cluster.getCurrentDir(0, JID), "paxos");
+    File paxos1 = new File(cluster.getCurrentDir(1, JID), "paxos");
+    File paxos2 = new File(cluster.getCurrentDir(2, JID), "paxos");
+    
+    GenericTestUtils.assertGlobEquals(paxos0, ".*", "101");
+    GenericTestUtils.assertGlobEquals(paxos1, ".*");
+    GenericTestUtils.assertGlobEquals(paxos2, ".*");
+  }
+  
+  /**
+   * Test an edge case discovered by randomized testing.
+   * 
+   * Starts with the edge case state set up by
+   * {@link #setupEdgeCaseOneJnHasSegmentWithAcceptedRecovery()}
+   * 
+   * Recovery 2:
+   * - New NN starts recovery and only talks to JN1 and JN2. JN0 has
+   *   crashed. Since they have no logs open, they say they don't need
+   *   recovery.
+   * - Starts writing segment 101, and writes 50 transactions before crashing.
+   *
+   * Recovery 3:
+   * - JN0 has come back to life.
+   * - New NN starts recovery and talks to all three. All three have
+   *   segments open from txid 101, so it calls prepareRecovery(101)
+   * - JN0 has an already-accepted value for segment 101, so it replies
+   *   "you should recover 101-101"
+   * - Former incorrect behavior: NN truncates logs to txid 101 even though
+   *   it should have recovered through 150.
+   *   
+   * In this case, even though there is an accepted recovery decision,
+   * the newer log segments should take precedence, since they were written
+   * in a newer epoch than the recorded decision.
+   */
+  @Test
+  public void testNewerVersionOfSegmentWins() throws Exception {
+    setupEdgeCaseOneJnHasSegmentWithAcceptedRecovery();
+    
+    // Now start writing again without JN0 present:
+    cluster.getJournalNode(0).stopAndJoin(0);
+    
+    qjm = createSpyingQJM();
+    try {
+      assertEquals(100, QJMTestUtil.recoverAndReturnLastTxn(qjm));
+      
+      // Write segment but do not finalize
+      writeSegment(cluster, qjm, 101, 50, false);
+    } finally {
+      qjm.close();
+    }
+    
+    // Now try to recover a new writer, with JN0 present,
+    // and ensure that all of the above-written transactions are recovered.
+    cluster.restartJournalNode(0);
+    qjm = createSpyingQJM();
+    try {
+      assertEquals(150, QJMTestUtil.recoverAndReturnLastTxn(qjm));
+    } finally {
+      qjm.close();
+    }
+  }
+  
+  /**
+   * Test another edge case discovered by randomized testing.
+   * 
+   * Starts with the edge case state set up by
+   * {@link #setupEdgeCaseOneJnHasSegmentWithAcceptedRecovery()}
+   * 
+   * Recovery 2:
+   * - New NN starts recovery and only talks to JN1 and JN2. JN0 has
+   *   crashed. Since they have no logs open, they say they don't need
+   *   recovery.
+   * - Before writing any transactions, JN0 comes back to life and
+   *   JN1 crashes.
+   * - Starts writing segment 101, and writes 50 transactions before crashing.
+   *
+   * Recovery 3:
+   * - JN1 has come back to life. JN2 crashes.
+   * - New NN starts recovery and talks to all three. All three have
+   *   segments open from txid 101, so it calls prepareRecovery(101)
+   * - JN0 has an already-accepted value for segment 101, so it replies
+   *   "you should recover 101-101"
+   * - Former incorrect behavior: NN truncates logs to txid 101 even though
+   *   it should have recovered through 150.
+   *   
+   * In this case, even though there is an accepted recovery decision,
+   * the newer log segments should take precedence, since they were written
+   * in a newer epoch than the recorded decision.
+   */
+  @Test
+  public void testNewerVersionOfSegmentWins2() throws Exception {
+    setupEdgeCaseOneJnHasSegmentWithAcceptedRecovery();
+
+    // Recover without JN0 present.
+    cluster.getJournalNode(0).stopAndJoin(0);
+    
+    qjm = createSpyingQJM();
+    try {
+      assertEquals(100, QJMTestUtil.recoverAndReturnLastTxn(qjm));
+
+      // After recovery, JN0 comes back to life and JN1 crashes.
+      cluster.restartJournalNode(0);
+      cluster.getJournalNode(1).stopAndJoin(0);
+      
+      // Write segment but do not finalize
+      writeSegment(cluster, qjm, 101, 50, false);
+    } finally {
+      qjm.close();
+    }
+    
+    // State:
+    // JN0: 1-100 finalized, 101_inprogress (txns up to 150)
+    // Previously, JN0 had an accepted recovery 101-101 from an earlier recovery
+    // attempt.
+    // JN1: 1-100 finalized
+    // JN2: 1-100 finalized, 101_inprogress (txns up to 150)
+    
+    // We need to test that the accepted recovery 101-101 on JN0 doesn't
+    // end up truncating the log back to 101.
+
+    cluster.restartJournalNode(1);
+    cluster.getJournalNode(2).stopAndJoin(0);
+
+    qjm = createSpyingQJM();
+    try {
+      assertEquals(150, QJMTestUtil.recoverAndReturnLastTxn(qjm));
+    } finally {
+      qjm.close();
+    }
+  }
+  
+  @Test(timeout=20000)
+  public void testCrashBetweenSyncLogAndPersistPaxosData() throws Exception {
+    JournalFaultInjector faultInjector =
+        JournalFaultInjector.instance = Mockito.mock(JournalFaultInjector.class);
+
+    setupLoggers345();
+
+    // Run recovery where the client only talks to JN0, JN1, such that it
+    // decides that the correct length is through txid 4.
+    // Only allow it to call acceptRecovery() on JN0.
+    qjm = createSpyingQJM();
+    spies = qjm.getLoggerSetForTests().getLoggersForTests();    
+    cluster.getJournalNode(2).stopAndJoin(0);
+    injectIOE().when(spies.get(1)).acceptRecovery(
+        Mockito.<SegmentStateProto>any(), Mockito.<URL>any());
+    
+    tryRecoveryExpectingFailure();
+
+    cluster.restartJournalNode(2);
+    
+    // State at this point:
+    // JN0: edit log for 1-4, paxos recovery data for txid 4
+    // JN1: edit log for 1-4,
+    // JN2: edit log for 1-5
+    
+    // Run recovery again, but don't allow JN0 to respond to the
+    // prepareRecovery() call. This will cause recovery to decide
+    // on txid 5.
+    // Additionally, crash all of the nodes before they persist
+    // any new paxos data.
+    qjm = createSpyingQJM();
+    spies = qjm.getLoggerSetForTests().getLoggersForTests();    
+    injectIOE().when(spies.get(0)).prepareRecovery(Mockito.eq(1L));
+
+    Mockito.doThrow(new IOException("Injected")).when(faultInjector)
+      .beforePersistPaxosData();
+    tryRecoveryExpectingFailure();
+    Mockito.reset(faultInjector);
+    
+    // State at this point:
+    // JN0: edit log for 1-5, paxos recovery data for txid 4
+    // !!!   This is the interesting bit, above. The on-disk data and the
+    //       paxos data don't match up!
+    // JN1: edit log for 1-5,
+    // JN2: edit log for 1-5,
+
+    // Now, stop JN2, and see if we can still start up even though
+    // JN0 is in a strange state where its log data is actually newer
+    // than its accepted Paxos state.
+
+    cluster.getJournalNode(2).stopAndJoin(0);
+    
+    qjm = createSpyingQJM();
+    try {
+      long recovered = QJMTestUtil.recoverAndReturnLastTxn(qjm);
+      assertTrue(recovered >= 4); // 4 was committed to a quorum
+    } finally {
+      qjm.close();
+    }
+  }
+  
+  private void tryRecoveryExpectingFailure() throws IOException {
+    try {
+      QJMTestUtil.recoverAndReturnLastTxn(qjm);
+      fail("Expected to fail recovery");
+    } catch (QuorumException qe) {
+      GenericTestUtils.assertExceptionContains("Injected", qe);
+    } finally {
+      qjm.close();
+    }
+
+  }
+  
+  private Stubber injectIOE() {
+    return futureThrows(new IOException("Injected"));
+  }
+
+  @Test
+  public void testPurgeLogs() throws Exception {
+    for (int txid = 1; txid <= 5; txid++) {
+      writeSegment(cluster, qjm, txid, 1, true);
+    }
+    File curDir = cluster.getCurrentDir(0, JID);
+    GenericTestUtils.assertGlobEquals(curDir, "edits_.*",
+        NNStorage.getFinalizedEditsFileName(1, 1),
+        NNStorage.getFinalizedEditsFileName(2, 2),
+        NNStorage.getFinalizedEditsFileName(3, 3),
+        NNStorage.getFinalizedEditsFileName(4, 4),
+        NNStorage.getFinalizedEditsFileName(5, 5));
+    File paxosDir = new File(curDir, "paxos");
+    GenericTestUtils.assertExists(paxosDir);
+
+    // Create new files in the paxos directory, which should get purged too.
+    assertTrue(new File(paxosDir, "1").createNewFile());
+    assertTrue(new File(paxosDir, "3").createNewFile());
+    
+    GenericTestUtils.assertGlobEquals(paxosDir, "\\d+",
+        "1", "3");
+    
+    // Create some temporary files of the sort that are used during recovery.
+    assertTrue(new File(curDir,
+        "edits_inprogress_0000000000000000001.epoch=140").createNewFile());
+    assertTrue(new File(curDir,
+        "edits_inprogress_0000000000000000002.empty").createNewFile());
+    
+    qjm.purgeLogsOlderThan(3);
+    
+    // Log purging is asynchronous, so we have to wait for the calls
+    // to be sent and respond before verifying.
+    waitForAllPendingCalls(qjm.getLoggerSetForTests());
+    
+    // Older edits should be purged
+    GenericTestUtils.assertGlobEquals(curDir, "edits_.*",
+        NNStorage.getFinalizedEditsFileName(3, 3),
+        NNStorage.getFinalizedEditsFileName(4, 4),
+        NNStorage.getFinalizedEditsFileName(5, 5));
+   
+    // Older paxos files should be purged
+    GenericTestUtils.assertGlobEquals(paxosDir, "\\d+",
+        "3");
+  }
+  
+  @Test
+  public void testToString() throws Exception {
+    GenericTestUtils.assertMatches(
+        qjm.toString(),
+        "QJM to \\[127.0.0.1:\\d+, 127.0.0.1:\\d+, 127.0.0.1:\\d+\\]");
+  }
+  
+  
+  private QuorumJournalManager createSpyingQJM()
+      throws IOException, URISyntaxException {
+    AsyncLogger.Factory spyFactory = new AsyncLogger.Factory() {
+      @Override
+      public AsyncLogger createLogger(Configuration conf, NamespaceInfo nsInfo,
+          String journalId, InetSocketAddress addr) {
+        AsyncLogger logger = new IPCLoggerChannel(conf, nsInfo, journalId, addr) {
+          protected ExecutorService createExecutor() {
+            // Don't parallelize calls to the quorum in the tests.
+            // This makes the tests more deterministic.
+            return MoreExecutors.sameThreadExecutor();
+          }
+        };
+        
+        return Mockito.spy(logger);
+      }
+    };
+    return new QuorumJournalManager(
+        conf, cluster.getQuorumJournalURI(JID), FAKE_NSINFO, spyFactory);
+  }
+
+  private static void waitForAllPendingCalls(AsyncLoggerSet als)
+      throws InterruptedException {
+    for (AsyncLogger l : als.getLoggersForTests()) {
+      IPCLoggerChannel ch = (IPCLoggerChannel)l;
+      ch.waitForAllPendingCalls();
+    }
+  }
+
+  private void checkRecovery(MiniJournalCluster cluster,
+      long segmentTxId, long expectedEndTxId)
+      throws IOException {
+    int numFinalized = 0;
+    for (int i = 0; i < cluster.getNumNodes(); i++) {
+      File logDir = cluster.getCurrentDir(i, JID);
+      EditLogFile elf = FileJournalManager.getLogFile(logDir, segmentTxId);
+      if (elf == null) {
+        continue;
+      }
+      if (!elf.isInProgress()) {
+        numFinalized++;
+        if (elf.getLastTxId() != expectedEndTxId) {
+          fail("File " + elf + " finalized to wrong txid, expected " +
+              expectedEndTxId);
+        }
+      }      
+    }
+    
+    if (numFinalized < cluster.getQuorumSize()) {
+      fail("Did not find a quorum of finalized logs starting at " +
+          segmentTxId);
+    }
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumJournalManagerUnit.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumJournalManagerUnit.java
new file mode 100644
index 0000000..295eab1
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestQuorumJournalManagerUnit.java
@@ -0,0 +1,200 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import static org.junit.Assert.fail;
+import static org.mockito.Matchers.anyLong;
+import static org.mockito.Matchers.eq;
+
+import java.io.IOException;
+import java.net.URI;
+import java.util.List;
+
+import org.apache.commons.logging.impl.Log4JLogger;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.qjournal.client.AsyncLogger;
+import org.apache.hadoop.hdfs.qjournal.client.QuorumException;
+import org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.GetJournalStateResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.apache.log4j.Level;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.stubbing.Stubber;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.SettableFuture;
+
+import static org.apache.hadoop.hdfs.qjournal.QJMTestUtil.writeOp;
+
+/**
+ * True unit tests for QuorumJournalManager
+ */
+public class TestQuorumJournalManagerUnit {
+  static {
+    ((Log4JLogger)QuorumJournalManager.LOG).getLogger().setLevel(Level.ALL);
+  }
+  private static final NamespaceInfo FAKE_NSINFO = new NamespaceInfo(
+      12345, "mycluster", "my-bp", 0L);
+
+  private Configuration conf = new Configuration();
+  private List<AsyncLogger> spyLoggers;
+  private QuorumJournalManager qjm;
+  
+  @Before
+  public void setup() throws Exception {
+    spyLoggers = ImmutableList.of(
+        mockLogger(),
+        mockLogger(),
+        mockLogger());
+
+    qjm = new QuorumJournalManager(conf, new URI("qjournal://host/jid"), FAKE_NSINFO) {
+      @Override
+      protected List<AsyncLogger> createLoggers(AsyncLogger.Factory factory) {
+        return spyLoggers;
+      }
+    };
+
+    for (AsyncLogger logger : spyLoggers) {
+      futureReturns(GetJournalStateResponseProto.newBuilder()
+          .setLastPromisedEpoch(0)
+          .setHttpPort(-1)
+          .build())
+        .when(logger).getJournalState();
+      
+      futureReturns(
+          NewEpochResponseProto.newBuilder().build()
+          ).when(logger).newEpoch(Mockito.anyLong());
+      
+      futureReturns(null).when(logger).format(Mockito.<NamespaceInfo>any());
+    }
+    
+    qjm.recoverUnfinalizedSegments();
+  }
+  
+  private AsyncLogger mockLogger() {
+    return Mockito.mock(AsyncLogger.class);
+  }
+  
+  static <V> Stubber futureReturns(V value) {
+    ListenableFuture<V> ret = Futures.immediateFuture(value);
+    return Mockito.doReturn(ret);
+  }
+  
+  static Stubber futureThrows(Throwable t) {
+    ListenableFuture<?> ret = Futures.immediateFailedFuture(t);
+    return Mockito.doReturn(ret);
+  }
+
+
+  @Test
+  public void testAllLoggersStartOk() throws Exception {
+    futureReturns(null).when(spyLoggers.get(0)).startLogSegment(Mockito.anyLong());
+    futureReturns(null).when(spyLoggers.get(1)).startLogSegment(Mockito.anyLong());
+    futureReturns(null).when(spyLoggers.get(2)).startLogSegment(Mockito.anyLong());
+    qjm.startLogSegment(1);
+  }
+
+  @Test
+  public void testQuorumOfLoggersStartOk() throws Exception {
+    futureReturns(null).when(spyLoggers.get(0)).startLogSegment(Mockito.anyLong());
+    futureReturns(null).when(spyLoggers.get(1)).startLogSegment(Mockito.anyLong());
+    futureThrows(new IOException("logger failed"))
+      .when(spyLoggers.get(2)).startLogSegment(Mockito.anyLong());
+    qjm.startLogSegment(1);
+  }
+  
+  @Test
+  public void testQuorumOfLoggersFail() throws Exception {
+    futureReturns(null).when(spyLoggers.get(0)).startLogSegment(Mockito.anyLong());
+    futureThrows(new IOException("logger failed"))
+    .when(spyLoggers.get(1)).startLogSegment(Mockito.anyLong());
+    futureThrows(new IOException("logger failed"))
+      .when(spyLoggers.get(2)).startLogSegment(Mockito.anyLong());
+    try {
+      qjm.startLogSegment(1);
+      fail("Did not throw when quorum failed");
+    } catch (QuorumException qe) {
+      GenericTestUtils.assertExceptionContains("logger failed", qe);
+    }
+  }
+  
+  @Test
+  public void testWriteEdits() throws Exception {
+    EditLogOutputStream stm = createLogSegment();
+    writeOp(stm, 1);
+    writeOp(stm, 2);
+    
+    stm.setReadyToFlush();
+    writeOp(stm, 3);
+    
+    // The flush should log txn 1-2
+    futureReturns(null).when(spyLoggers.get(0)).sendEdits(
+        anyLong(), eq(1L), eq(2), Mockito.<byte[]>any());
+    futureReturns(null).when(spyLoggers.get(1)).sendEdits(
+        anyLong(), eq(1L), eq(2), Mockito.<byte[]>any());
+    futureReturns(null).when(spyLoggers.get(2)).sendEdits(
+        anyLong(), eq(1L), eq(2), Mockito.<byte[]>any());
+    stm.flush();
+
+    // Another flush should now log txn #3
+    stm.setReadyToFlush();
+    futureReturns(null).when(spyLoggers.get(0)).sendEdits(
+        anyLong(), eq(3L), eq(1), Mockito.<byte[]>any());
+    futureReturns(null).when(spyLoggers.get(1)).sendEdits(
+        anyLong(), eq(3L), eq(1), Mockito.<byte[]>any());
+    futureReturns(null).when(spyLoggers.get(2)).sendEdits(
+        anyLong(), eq(3L), eq(1), Mockito.<byte[]>any());
+    stm.flush();
+  }
+  
+  @Test
+  public void testWriteEditsOneSlow() throws Exception {
+    EditLogOutputStream stm = createLogSegment();
+    writeOp(stm, 1);
+    stm.setReadyToFlush();
+    
+    // Make the first two logs respond immediately
+    futureReturns(null).when(spyLoggers.get(0)).sendEdits(
+        anyLong(), eq(1L), eq(1), Mockito.<byte[]>any());
+    futureReturns(null).when(spyLoggers.get(1)).sendEdits(
+        anyLong(), eq(1L), eq(1), Mockito.<byte[]>any());
+    
+    // And the third log not respond
+    SettableFuture<Void> slowLog = SettableFuture.<Void>create();
+    Mockito.doReturn(slowLog).when(spyLoggers.get(2)).sendEdits(
+        anyLong(), eq(1L), eq(1), Mockito.<byte[]>any());
+    stm.flush();
+    
+    Mockito.verify(spyLoggers.get(0)).setCommittedTxId(1L);
+  }
+
+  private EditLogOutputStream createLogSegment() throws IOException {
+    futureReturns(null).when(spyLoggers.get(0)).startLogSegment(Mockito.anyLong());
+    futureReturns(null).when(spyLoggers.get(1)).startLogSegment(Mockito.anyLong());
+    futureReturns(null).when(spyLoggers.get(2)).startLogSegment(Mockito.anyLong());
+    EditLogOutputStream stm = qjm.startLogSegment(1);
+    return stm;
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestSegmentRecoveryComparator.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestSegmentRecoveryComparator.java
new file mode 100644
index 0000000..ecd6a2c
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestSegmentRecoveryComparator.java
@@ -0,0 +1,94 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.client;
+
+import static org.junit.Assert.*;
+
+import java.util.Map;
+import java.util.Map.Entry;
+
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.SegmentStateProto;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import com.google.common.collect.Maps;
+
+import static org.apache.hadoop.hdfs.qjournal.client.SegmentRecoveryComparator.INSTANCE;
+
+public class TestSegmentRecoveryComparator {
+  
+  private static Map.Entry<AsyncLogger, PrepareRecoveryResponseProto> makeEntry(
+      PrepareRecoveryResponseProto proto) {
+    return Maps.immutableEntry(Mockito.mock(AsyncLogger.class), proto);
+  }
+  
+  @Test
+  public void testComparisons() {
+    Entry<AsyncLogger, PrepareRecoveryResponseProto> INPROGRESS_1_3 =
+        makeEntry(PrepareRecoveryResponseProto.newBuilder()
+          .setSegmentState(SegmentStateProto.newBuilder()
+              .setStartTxId(1L)
+              .setEndTxId(3L)
+              .setIsInProgress(true))
+          .setLastWriterEpoch(0L)
+          .build());
+    Entry<AsyncLogger, PrepareRecoveryResponseProto> INPROGRESS_1_4 =
+        makeEntry(PrepareRecoveryResponseProto.newBuilder()
+          .setSegmentState(SegmentStateProto.newBuilder()
+              .setStartTxId(1L)
+              .setEndTxId(4L)
+              .setIsInProgress(true))
+          .setLastWriterEpoch(0L)
+          .build());
+    Entry<AsyncLogger, PrepareRecoveryResponseProto> INPROGRESS_1_4_ACCEPTED =
+        makeEntry(PrepareRecoveryResponseProto.newBuilder()
+          .setSegmentState(SegmentStateProto.newBuilder()
+              .setStartTxId(1L)
+              .setEndTxId(4L)
+              .setIsInProgress(true))
+          .setLastWriterEpoch(0L)
+          .setAcceptedInEpoch(1L)
+          .build());
+
+    Entry<AsyncLogger, PrepareRecoveryResponseProto> FINALIZED_1_3 =
+        makeEntry(PrepareRecoveryResponseProto.newBuilder()
+          .setSegmentState(SegmentStateProto.newBuilder()
+              .setStartTxId(1L)
+              .setEndTxId(3L)
+              .setIsInProgress(false))
+          .setLastWriterEpoch(0L)
+          .build());
+
+    // Should compare equal to itself
+    assertEquals(0, INSTANCE.compare(INPROGRESS_1_3, INPROGRESS_1_3));
+    
+    // Longer log wins.
+    assertEquals(-1, INSTANCE.compare(INPROGRESS_1_3, INPROGRESS_1_4));
+    assertEquals(1, INSTANCE.compare(INPROGRESS_1_4, INPROGRESS_1_3));
+    
+    // Finalized log wins even over a longer in-progress
+    assertEquals(-1, INSTANCE.compare(INPROGRESS_1_4, FINALIZED_1_3));
+    assertEquals(1, INSTANCE.compare(FINALIZED_1_3, INPROGRESS_1_4));
+
+    // Finalized log wins even if the in-progress one has an accepted
+    // recovery proposal.
+    assertEquals(-1, INSTANCE.compare(INPROGRESS_1_4_ACCEPTED, FINALIZED_1_3));
+    assertEquals(1, INSTANCE.compare(FINALIZED_1_3, INPROGRESS_1_4_ACCEPTED));
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/server/TestJournal.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/server/TestJournal.java
new file mode 100644
index 0000000..c9db35f
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/server/TestJournal.java
@@ -0,0 +1,361 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import static org.junit.Assert.*;
+
+import java.io.File;
+import java.io.IOException;
+
+import org.apache.hadoop.fs.FileUtil;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.qjournal.QJMTestUtil;
+import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
+import org.apache.hadoop.hdfs.qjournal.protocol.JournalOutOfSyncException;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProtoOrBuilder;
+import org.apache.hadoop.hdfs.qjournal.server.Journal;
+import org.apache.hadoop.hdfs.server.common.Storage.StorageDirectory;
+import org.apache.hadoop.hdfs.server.common.Storage;
+import org.apache.hadoop.hdfs.server.common.StorageErrorReporter;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.junit.After;
+import org.junit.Assume;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+public class TestJournal {
+  private static final NamespaceInfo FAKE_NSINFO = new NamespaceInfo(
+      12345, "mycluster", "my-bp", 0L);
+  private static final NamespaceInfo FAKE_NSINFO_2 = new NamespaceInfo(
+      6789, "mycluster", "my-bp", 0L);
+  
+  private static final String JID = "test-journal";
+
+  private static final File TEST_LOG_DIR = new File(
+      new File(MiniDFSCluster.getBaseDirectory()), "TestJournal");
+
+  private StorageErrorReporter mockErrorReporter = Mockito.mock(
+      StorageErrorReporter.class);
+
+  private Journal journal;
+
+  
+  @Before
+  public void setup() throws Exception {
+    FileUtil.fullyDelete(TEST_LOG_DIR);
+    journal = new Journal(TEST_LOG_DIR, JID, mockErrorReporter);
+    journal.format(FAKE_NSINFO);
+  }
+  
+  @After
+  public void verifyNoStorageErrors() throws Exception{
+    Mockito.verify(mockErrorReporter, Mockito.never())
+      .reportErrorOnFile(Mockito.<File>any());
+  }
+  
+  @After
+  public void cleanup() {
+    IOUtils.closeStream(journal);
+  }
+  
+  @Test
+  public void testEpochHandling() throws Exception {
+    assertEquals(0, journal.getLastPromisedEpoch());
+    NewEpochResponseProto newEpoch =
+        journal.newEpoch(FAKE_NSINFO, 1);
+    assertFalse(newEpoch.hasLastSegmentTxId());
+    assertEquals(1, journal.getLastPromisedEpoch());
+    journal.newEpoch(FAKE_NSINFO, 3);
+    assertFalse(newEpoch.hasLastSegmentTxId());
+    assertEquals(3, journal.getLastPromisedEpoch());
+    try {
+      journal.newEpoch(FAKE_NSINFO, 3);
+      fail("Should have failed to promise same epoch twice");
+    } catch (IOException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "Proposed epoch 3 <= last promise 3", ioe);
+    }
+    try {
+      journal.startLogSegment(makeRI(1), 12345L);
+      fail("Should have rejected call from prior epoch");
+    } catch (IOException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "epoch 1 is less than the last promised epoch 3", ioe);
+    }
+    try {
+      journal.journal(makeRI(1), 12345L, 100L, 0, new byte[0]);
+      fail("Should have rejected call from prior epoch");
+    } catch (IOException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "epoch 1 is less than the last promised epoch 3", ioe);
+    }
+  }
+  
+  @Test
+  public void testMaintainCommittedTxId() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 1);
+    journal.startLogSegment(makeRI(1), 1);
+    // Send txids 1-3, with a request indicating only 0 committed
+    journal.journal(new RequestInfo(JID, 1, 2, 0), 1, 1, 3,
+        QJMTestUtil.createTxnData(1, 3));
+    assertEquals(0, journal.getCommittedTxnIdForTests());
+    
+    // Send 4-6, with request indicating that through 3 is committed.
+    journal.journal(new RequestInfo(JID, 1, 3, 3), 1, 4, 3,
+        QJMTestUtil.createTxnData(4, 6));
+    assertEquals(3, journal.getCommittedTxnIdForTests());    
+  }
+  
+  @Test
+  public void testRestartJournal() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 1);
+    journal.startLogSegment(makeRI(1), 1);
+    journal.journal(makeRI(2), 1, 1, 2, 
+        QJMTestUtil.createTxnData(1, 2));
+    // Don't finalize.
+    
+    String storageString = journal.getStorage().toColonSeparatedString();
+    System.err.println("storage string: " + storageString);
+    journal.close(); // close to unlock the storage dir
+    
+    // Now re-instantiate, make sure history is still there
+    journal = new Journal(TEST_LOG_DIR, JID, mockErrorReporter);
+    
+    // The storage info should be read, even if no writer has taken over.
+    assertEquals(storageString,
+        journal.getStorage().toColonSeparatedString());
+
+    assertEquals(1, journal.getLastPromisedEpoch());
+    NewEpochResponseProtoOrBuilder newEpoch = journal.newEpoch(FAKE_NSINFO, 2);
+    assertEquals(1, newEpoch.getLastSegmentTxId());
+  }
+  
+  @Test
+  public void testFormatResetsCachedValues() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 12345L);
+    journal.startLogSegment(new RequestInfo(JID, 12345L, 1L, 0L), 1L);
+
+    assertEquals(12345L, journal.getLastPromisedEpoch());
+    assertEquals(12345L, journal.getLastWriterEpoch());
+    assertTrue(journal.isFormatted());
+    
+    journal.format(FAKE_NSINFO_2);
+    
+    assertEquals(0, journal.getLastPromisedEpoch());
+    assertEquals(0, journal.getLastWriterEpoch());
+    assertTrue(journal.isFormatted());
+  }
+  
+  /**
+   * Test that, if the writer crashes at the very beginning of a segment,
+   * before any transactions are written, that the next newEpoch() call
+   * returns the prior segment txid as its most recent segment.
+   */
+  @Test
+  public void testNewEpochAtBeginningOfSegment() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 1);
+    journal.startLogSegment(makeRI(1), 1);
+    journal.journal(makeRI(2), 1, 1, 2, 
+        QJMTestUtil.createTxnData(1, 2));
+    journal.finalizeLogSegment(makeRI(3), 1, 2);
+    journal.startLogSegment(makeRI(4), 3);
+    NewEpochResponseProto resp = journal.newEpoch(FAKE_NSINFO, 2);
+    assertEquals(1, resp.getLastSegmentTxId());
+  }
+  
+  @Test
+  public void testJournalLocking() throws Exception {
+    Assume.assumeTrue(journal.getStorage().getStorageDir(0).isLockSupported());
+    StorageDirectory sd = journal.getStorage().getStorageDir(0);
+    File lockFile = new File(sd.getRoot(), Storage.STORAGE_FILE_LOCK);
+    
+    // Journal should be locked, since the format() call locks it.
+    GenericTestUtils.assertExists(lockFile);
+
+    journal.newEpoch(FAKE_NSINFO,  1);
+    try {
+      new Journal(TEST_LOG_DIR, JID, mockErrorReporter);
+      fail("Did not fail to create another journal in same dir");
+    } catch (IOException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "Cannot lock storage", ioe);
+    }
+    
+    journal.close();
+    
+    // Journal should no longer be locked after the close() call.
+    // Hence, should be able to create a new Journal in the same dir.
+    Journal journal2 = new Journal(TEST_LOG_DIR, JID, mockErrorReporter);
+    journal2.newEpoch(FAKE_NSINFO, 2);
+  }
+  
+  /**
+   * Test finalizing a segment after some batch of edits were missed.
+   * This should fail, since we validate the log before finalization.
+   */
+  @Test
+  public void testFinalizeWhenEditsAreMissed() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 1);
+    journal.startLogSegment(makeRI(1), 1);
+    journal.journal(makeRI(2), 1, 1, 3,
+        QJMTestUtil.createTxnData(1, 3));
+    
+    // Try to finalize up to txn 6, even though we only wrote up to txn 3.
+    try {
+      journal.finalizeLogSegment(makeRI(3), 1, 6);
+      fail("did not fail to finalize");
+    } catch (JournalOutOfSyncException e) {
+      GenericTestUtils.assertExceptionContains(
+          "but only written up to txid 3", e);
+    }
+    
+    // Check that, even if we re-construct the journal by scanning the
+    // disk, we don't allow finalizing incorrectly.
+    journal.close();
+    journal = new Journal(TEST_LOG_DIR, JID, mockErrorReporter);
+    
+    try {
+      journal.finalizeLogSegment(makeRI(4), 1, 6);
+      fail("did not fail to finalize");
+    } catch (JournalOutOfSyncException e) {
+      GenericTestUtils.assertExceptionContains(
+          "disk only contains up to txid 3", e);
+    }
+  }
+  
+  /**
+   * Ensure that finalizing a segment which doesn't exist throws the
+   * appropriate exception.
+   */
+  @Test
+  public void testFinalizeMissingSegment() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 1);
+    try {
+      journal.finalizeLogSegment(makeRI(1), 1000, 1001);
+      fail("did not fail to finalize");
+    } catch (JournalOutOfSyncException e) {
+      GenericTestUtils.assertExceptionContains(
+          "No log file to finalize at transaction ID 1000", e);
+    }
+  }
+
+  /**
+   * Assume that a client is writing to a journal, but loses its connection
+   * in the middle of a segment. Thus, any future journal() calls in that
+   * segment may fail, because some txns were missed while the connection was
+   * down.
+   *
+   * Eventually, the connection comes back, and the NN tries to start a new
+   * segment at a higher txid. This should abort the old one and succeed.
+   */
+  @Test
+  public void testAbortOldSegmentIfFinalizeIsMissed() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 1);
+    
+    // Start a segment at txid 1, and write a batch of 3 txns.
+    journal.startLogSegment(makeRI(1), 1);
+    journal.journal(makeRI(2), 1, 1, 3,
+        QJMTestUtil.createTxnData(1, 3));
+
+    GenericTestUtils.assertExists(
+        journal.getStorage().getInProgressEditLog(1));
+    
+    // Try to start new segment at txid 6, this should abort old segment and
+    // then succeed, allowing us to write txid 6-9.
+    journal.startLogSegment(makeRI(3), 6);
+    journal.journal(makeRI(4), 6, 6, 3,
+        QJMTestUtil.createTxnData(6, 3));
+
+    // The old segment should *not* be finalized.
+    GenericTestUtils.assertExists(
+        journal.getStorage().getInProgressEditLog(1));
+    GenericTestUtils.assertExists(
+        journal.getStorage().getInProgressEditLog(6));
+  }
+  
+  /**
+   * Test behavior of startLogSegment() when a segment with the
+   * same transaction ID already exists.
+   */
+  @Test
+  public void testStartLogSegmentWhenAlreadyExists() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 1);
+    
+    // Start a segment at txid 1, and write just 1 transaction. This
+    // would normally be the START_LOG_SEGMENT transaction.
+    journal.startLogSegment(makeRI(1), 1);
+    journal.journal(makeRI(2), 1, 1, 1,
+        QJMTestUtil.createTxnData(1, 1));
+    
+    // Try to start new segment at txid 1, this should succeed, because
+    // we are allowed to re-start a segment if we only ever had the
+    // START_LOG_SEGMENT transaction logged.
+    journal.startLogSegment(makeRI(3), 1);
+    journal.journal(makeRI(4), 1, 1, 1,
+        QJMTestUtil.createTxnData(1, 1));
+
+    // This time through, write more transactions afterwards, simulating
+    // real user transactions.
+    journal.journal(makeRI(5), 1, 2, 3,
+        QJMTestUtil.createTxnData(2, 3));
+
+    try {
+      journal.startLogSegment(makeRI(6), 1);
+      fail("Did not fail to start log segment which would overwrite " +
+          "an existing one");
+    } catch (IllegalStateException ise) {
+      GenericTestUtils.assertExceptionContains(
+          "seems to contain valid transactions", ise);
+    }
+    
+    journal.finalizeLogSegment(makeRI(7), 1, 4);
+    
+    // Ensure that we cannot overwrite a finalized segment
+    try {
+      journal.startLogSegment(makeRI(8), 1);
+      fail("Did not fail to start log segment which would overwrite " +
+          "an existing one");
+    } catch (IllegalStateException ise) {
+      GenericTestUtils.assertExceptionContains(
+          "have a finalized segment", ise);
+    }
+
+  }
+  
+  private static RequestInfo makeRI(int serial) {
+    return new RequestInfo(JID, 1, serial, 0);
+  }
+  
+  @Test
+  public void testNamespaceVerification() throws Exception {
+    journal.newEpoch(FAKE_NSINFO, 1);
+
+    try {
+      journal.newEpoch(FAKE_NSINFO_2, 2);
+      fail("Did not fail newEpoch() when namespaces mismatched");
+    } catch (IOException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "Incompatible namespaceID", ioe);
+    }
+  }
+
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/server/TestJournalNode.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/server/TestJournalNode.java
new file mode 100644
index 0000000..f57f7e6
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/server/TestJournalNode.java
@@ -0,0 +1,332 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.qjournal.server;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import java.io.File;
+import java.net.HttpURLConnection;
+import java.net.InetSocketAddress;
+import java.net.URL;
+import java.util.concurrent.ExecutionException;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileUtil;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.DFSTestUtil;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.protocol.HdfsConstants;
+import org.apache.hadoop.hdfs.qjournal.QJMTestUtil;
+import org.apache.hadoop.hdfs.qjournal.client.IPCLoggerChannel;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.NewEpochResponseProto;
+import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocolProtos.PrepareRecoveryResponseProto;
+import org.apache.hadoop.hdfs.qjournal.server.Journal;
+import org.apache.hadoop.hdfs.qjournal.server.JournalNode;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.metrics2.MetricsRecordBuilder;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.apache.hadoop.test.MetricsAsserts;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import com.google.common.base.Charsets;
+import com.google.common.base.Stopwatch;
+import com.google.common.primitives.Bytes;
+import com.google.common.primitives.Ints;
+
+
+public class TestJournalNode {
+  private static final NamespaceInfo FAKE_NSINFO = new NamespaceInfo(
+      12345, "mycluster", "my-bp", 0L);
+
+  private JournalNode jn;
+  private Journal journal; 
+  private Configuration conf = new Configuration();
+  private IPCLoggerChannel ch;
+  private String journalId;
+
+  static {
+    // Avoid an error when we double-initialize JvmMetrics
+    DefaultMetricsSystem.setMiniClusterMode(true);
+  }
+  
+  @Before
+  public void setup() throws Exception {
+    File editsDir = new File(MiniDFSCluster.getBaseDirectory() +
+        File.separator + "TestJournalNode");
+    FileUtil.fullyDelete(editsDir);
+    
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_KEY,
+        editsDir.getAbsolutePath());
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_RPC_ADDRESS_KEY,
+        "0.0.0.0:0");
+    jn = new JournalNode();
+    jn.setConf(conf);
+    jn.start();
+    journalId = "test-journalid-" + GenericTestUtils.uniqueSequenceId();
+    journal = jn.getOrCreateJournal(journalId);
+    journal.format(FAKE_NSINFO);
+    
+    ch = new IPCLoggerChannel(conf, FAKE_NSINFO, journalId, jn.getBoundIpcAddress());
+  }
+  
+  @After
+  public void teardown() throws Exception {
+    jn.stop(0);
+  }
+  
+  @Test
+  public void testJournal() throws Exception {
+    MetricsRecordBuilder metrics = MetricsAsserts.getMetrics(
+        journal.getMetricsForTests().getName());
+    MetricsAsserts.assertCounter("BatchesWritten", 0L, metrics);
+    MetricsAsserts.assertCounter("BatchesWrittenWhileLagging", 0L, metrics);
+    MetricsAsserts.assertGauge("CurrentLagTxns", 0L, metrics);
+
+    IPCLoggerChannel ch = new IPCLoggerChannel(
+        conf, FAKE_NSINFO, journalId, jn.getBoundIpcAddress());
+    ch.newEpoch(1).get();
+    ch.setEpoch(1);
+    ch.startLogSegment(1).get();
+    ch.sendEdits(1L, 1, 1, "hello".getBytes(Charsets.UTF_8)).get();
+    
+    metrics = MetricsAsserts.getMetrics(
+        journal.getMetricsForTests().getName());
+    MetricsAsserts.assertCounter("BatchesWritten", 1L, metrics);
+    MetricsAsserts.assertCounter("BatchesWrittenWhileLagging", 0L, metrics);
+    MetricsAsserts.assertGauge("CurrentLagTxns", 0L, metrics);
+
+    ch.setCommittedTxId(100L);
+    ch.sendEdits(1L, 2, 1, "goodbye".getBytes(Charsets.UTF_8)).get();
+
+    metrics = MetricsAsserts.getMetrics(
+        journal.getMetricsForTests().getName());
+    MetricsAsserts.assertCounter("BatchesWritten", 2L, metrics);
+    MetricsAsserts.assertCounter("BatchesWrittenWhileLagging", 1L, metrics);
+    MetricsAsserts.assertGauge("CurrentLagTxns", 98L, metrics);
+
+  }
+  
+  
+  @Test
+  public void testReturnsSegmentInfoAtEpochTransition() throws Exception {
+    ch.newEpoch(1).get();
+    ch.setEpoch(1);
+    ch.startLogSegment(1).get();
+    ch.sendEdits(1L, 1, 2, QJMTestUtil.createTxnData(1, 2)).get();
+    
+    // Switch to a new epoch without closing earlier segment
+    NewEpochResponseProto response = ch.newEpoch(2).get();
+    ch.setEpoch(2);
+    assertEquals(1, response.getLastSegmentTxId());
+    
+    ch.finalizeLogSegment(1, 2).get();
+    
+    // Switch to a new epoch after just closing the earlier segment.
+    response = ch.newEpoch(3).get();
+    ch.setEpoch(3);
+    assertEquals(1, response.getLastSegmentTxId());
+    
+    // Start a segment but don't write anything, check newEpoch segment info
+    ch.startLogSegment(3).get();
+    response = ch.newEpoch(4).get();
+    ch.setEpoch(4);
+    // Because the new segment is empty, it is equivalent to not having
+    // started writing it. Hence, we should return the prior segment txid.
+    assertEquals(1, response.getLastSegmentTxId());
+  }
+  
+  @Test
+  public void testHttpServer() throws Exception {
+    InetSocketAddress addr = jn.getBoundHttpAddress();
+    assertTrue(addr.getPort() > 0);
+    
+    String urlRoot = "http://localhost:" + addr.getPort();
+    
+    // Check default servlets.
+    String pageContents = DFSTestUtil.urlGet(new URL(urlRoot + "/jmx"));
+    assertTrue("Bad contents: " + pageContents,
+        pageContents.contains(
+            "Hadoop:service=JournalNode,name=JvmMetrics"));
+    
+    // Check JSP page.
+    pageContents = DFSTestUtil.urlGet(
+        new URL(urlRoot + "/journalstatus.jsp"));
+    assertTrue(pageContents.contains("JournalNode"));
+
+    // Create some edits on server side
+    byte[] EDITS_DATA = QJMTestUtil.createTxnData(1, 3);
+    IPCLoggerChannel ch = new IPCLoggerChannel(
+        conf, FAKE_NSINFO, journalId, jn.getBoundIpcAddress());
+    ch.newEpoch(1).get();
+    ch.setEpoch(1);
+    ch.startLogSegment(1).get();
+    ch.sendEdits(1L, 1, 3, EDITS_DATA).get();
+    ch.finalizeLogSegment(1, 3).get();
+
+    // Attempt to retrieve via HTTP, ensure we get the data back
+    // including the header we expected
+    byte[] retrievedViaHttp = DFSTestUtil.urlGetBytes(new URL(urlRoot +
+        "/getJournal?segmentTxId=1&jid=" + journalId));
+    byte[] expected = Bytes.concat(
+            Ints.toByteArray(HdfsConstants.LAYOUT_VERSION),
+            EDITS_DATA);
+
+    assertArrayEquals(expected, retrievedViaHttp);
+    
+    // Attempt to fetch a non-existent file, check that we get an
+    // error status code
+    URL badUrl = new URL(urlRoot + "/getJournal?segmentTxId=12345&jid=" + journalId);
+    HttpURLConnection connection = (HttpURLConnection)badUrl.openConnection();
+    try {
+      assertEquals(404, connection.getResponseCode());
+    } finally {
+      connection.disconnect();
+    }
+  }
+
+  /**
+   * Test that the JournalNode performs correctly as a Paxos
+   * <em>Acceptor</em> process.
+   */
+  @Test
+  public void testAcceptRecoveryBehavior() throws Exception {
+    // We need to run newEpoch() first, or else we have no way to distinguish
+    // different proposals for the same decision.
+    try {
+      ch.prepareRecovery(1L).get();
+      fail("Did not throw IllegalState when trying to run paxos without an epoch");
+    } catch (ExecutionException ise) {
+      GenericTestUtils.assertExceptionContains("bad epoch", ise);
+    }
+    
+    ch.newEpoch(1).get();
+    ch.setEpoch(1);
+    
+    // prepare() with no previously accepted value and no logs present
+    PrepareRecoveryResponseProto prep = ch.prepareRecovery(1L).get();
+    System.err.println("Prep: " + prep);
+    assertFalse(prep.hasAcceptedInEpoch());
+    assertFalse(prep.hasSegmentState());
+    
+    // Make a log segment, and prepare again -- this time should see the
+    // segment existing.
+    ch.startLogSegment(1L).get();
+    ch.sendEdits(1L, 1L, 1, QJMTestUtil.createTxnData(1, 1)).get();
+
+    prep = ch.prepareRecovery(1L).get();
+    System.err.println("Prep: " + prep);
+    assertFalse(prep.hasAcceptedInEpoch());
+    assertTrue(prep.hasSegmentState());
+    
+    // accept() should save the accepted value in persistent storage
+    ch.acceptRecovery(prep.getSegmentState(), new URL("file:///dev/null")).get();
+
+    // So another prepare() call from a new epoch would return this value
+    ch.newEpoch(2);
+    ch.setEpoch(2);
+    prep = ch.prepareRecovery(1L).get();
+    assertEquals(1L, prep.getAcceptedInEpoch());
+    assertEquals(1L, prep.getSegmentState().getEndTxId());
+    
+    // A prepare() or accept() call from an earlier epoch should now be rejected
+    ch.setEpoch(1);
+    try {
+      ch.prepareRecovery(1L).get();
+      fail("prepare from earlier epoch not rejected");
+    } catch (ExecutionException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "epoch 1 is less than the last promised epoch 2",
+          ioe);
+    }
+    try {
+      ch.acceptRecovery(prep.getSegmentState(), new URL("file:///dev/null")).get();
+      fail("accept from earlier epoch not rejected");
+    } catch (ExecutionException ioe) {
+      GenericTestUtils.assertExceptionContains(
+          "epoch 1 is less than the last promised epoch 2",
+          ioe);
+    }
+  }
+  
+  @Test
+  public void testFailToStartWithBadConfig() throws Exception {
+    Configuration conf = new Configuration();
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_KEY, "non-absolute-path");
+    assertJNFailsToStart(conf, "should be an absolute path");
+    
+    // Existing file which is not a directory 
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_KEY, "/dev/null");
+    assertJNFailsToStart(conf, "is not a directory");
+    
+    // Directory which cannot be created
+    conf.set(DFSConfigKeys.DFS_JOURNALNODE_EDITS_DIR_KEY, "/proc/does-not-exist");
+    assertJNFailsToStart(conf, "Could not create");
+
+  }
+
+  private static void assertJNFailsToStart(Configuration conf,
+      String errString) {
+    try {
+      JournalNode jn = new JournalNode();
+      jn.setConf(conf);
+      jn.start();
+    } catch (Exception e) {
+      GenericTestUtils.assertExceptionContains(errString, e);
+    }
+  }
+  
+  /**
+   * Simple test of how fast the code path is to write edits.
+   * This isn't a true unit test, but can be run manually to
+   * check performance.
+   * 
+   * At the time of development, this test ran in ~4sec on an
+   * SSD-enabled laptop (1.8ms/batch).
+   */
+  @Test(timeout=100000)
+  public void testPerformance() throws Exception {
+    doPerfTest(8192, 1024); // 8MB
+  }
+  
+  private void doPerfTest(int editsSize, int numEdits) throws Exception {
+    byte[] data = new byte[editsSize];
+    ch.newEpoch(1).get();
+    ch.setEpoch(1);
+    ch.startLogSegment(1).get();
+    
+    Stopwatch sw = new Stopwatch().start();
+    for (int i = 1; i < numEdits; i++) {
+      ch.sendEdits(1L, i, 1, data).get();
+    }
+    long time = sw.elapsedMillis();
+    
+    System.err.println("Wrote " + numEdits + " batches of " + editsSize +
+        " bytes in " + time + "ms");
+    float avgRtt = (float)time/(float)numEdits;
+    long throughput = ((long)numEdits * editsSize * 1000L)/time;
+    System.err.println("Time per batch: " + avgRtt + "ms");
+    System.err.println("Throughput: " + throughput + " bytes/sec");
+  }
+}
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/security/token/block/TestBlockToken.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/security/token/block/TestBlockToken.java
index f32b70d..6a9a071 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/security/token/block/TestBlockToken.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/security/token/block/TestBlockToken.java
@@ -74,6 +74,7 @@
 import org.apache.log4j.Level;
 import org.junit.Assert;
 import org.junit.Assume;
+import org.junit.Before;
 import org.junit.Test;
 import org.mockito.invocation.InvocationOnMock;
 import org.mockito.stubbing.Answer;
@@ -87,14 +88,6 @@
   public static final Log LOG = LogFactory.getLog(TestBlockToken.class);
   private static final String ADDRESS = "0.0.0.0";
 
-  static final String SERVER_PRINCIPAL_KEY = "test.ipc.server.principal";
-  private static Configuration conf;
-  static {
-    conf = new Configuration();
-    conf.set(HADOOP_SECURITY_AUTHENTICATION, "kerberos");
-    UserGroupInformation.setConfiguration(conf);
-  }
-
   static {
     ((Log4JLogger) Client.LOG).getLogger().setLevel(Level.ALL);
     ((Log4JLogger) Server.LOG).getLogger().setLevel(Level.ALL);
@@ -111,6 +104,13 @@
   ExtendedBlock block1 = new ExtendedBlock("0", 0L);
   ExtendedBlock block2 = new ExtendedBlock("10", 10L);
   ExtendedBlock block3 = new ExtendedBlock("-10", -108L);
+  
+  @Before
+  public void disableKerberos() {
+    Configuration conf = new Configuration();
+    conf.set(HADOOP_SECURITY_AUTHENTICATION, "simple");
+    UserGroupInformation.setConfiguration(conf);
+  }
 
   private static class GetLengthAnswer implements
       Answer<GetReplicaVisibleLengthResponseProto> {
@@ -215,8 +215,9 @@
     tokenGenerationAndVerification(masterHandler, slaveHandler);
   }
 
-  private Server createMockDatanode(BlockTokenSecretManager sm,
-      Token<BlockTokenIdentifier> token) throws IOException, ServiceException {
+  private static Server createMockDatanode(BlockTokenSecretManager sm,
+      Token<BlockTokenIdentifier> token, Configuration conf)
+      throws IOException, ServiceException {
     ClientDatanodeProtocolPB mockDN = mock(ClientDatanodeProtocolPB.class);
 
     BlockTokenIdentifier id = sm.createIdentifier();
@@ -238,12 +239,16 @@
 
   @Test
   public void testBlockTokenRpc() throws Exception {
+    Configuration conf = new Configuration();
+    conf.set(HADOOP_SECURITY_AUTHENTICATION, "kerberos");
+    UserGroupInformation.setConfiguration(conf);
+    
     BlockTokenSecretManager sm = new BlockTokenSecretManager(
         blockKeyUpdateInterval, blockTokenLifetime, 0, "fake-pool", null);
     Token<BlockTokenIdentifier> token = sm.generateToken(block3,
         EnumSet.allOf(BlockTokenSecretManager.AccessMode.class));
 
-    final Server server = createMockDatanode(sm, token);
+    final Server server = createMockDatanode(sm, token, conf);
 
     server.start();
 
@@ -272,13 +277,17 @@
    */
   @Test
   public void testBlockTokenRpcLeak() throws Exception {
+    Configuration conf = new Configuration();
+    conf.set(HADOOP_SECURITY_AUTHENTICATION, "kerberos");
+    UserGroupInformation.setConfiguration(conf);
+    
     Assume.assumeTrue(FD_DIR.exists());
     BlockTokenSecretManager sm = new BlockTokenSecretManager(
         blockKeyUpdateInterval, blockTokenLifetime, 0, "fake-pool", null);
     Token<BlockTokenIdentifier> token = sm.generateToken(block3,
         EnumSet.allOf(BlockTokenSecretManager.AccessMode.class));
 
-    final Server server = createMockDatanode(sm, token);
+    final Server server = createMockDatanode(sm, token, conf);
     server.start();
 
     final InetSocketAddress addr = NetUtils.getConnectAddress(server);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/NameNodeAdapter.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/NameNodeAdapter.java
index ada2e2a..f310959 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/NameNodeAdapter.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/NameNodeAdapter.java
@@ -17,11 +17,16 @@
  */
 package org.apache.hadoop.hdfs.server.namenode;
 
+import static org.mockito.Matchers.anyInt;
+import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.spy;
+
 import java.io.File;
 import java.io.IOException;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 
 import org.apache.hadoop.fs.UnresolvedLinkException;
+import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.fs.permission.PermissionStatus;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.HdfsFileStatus;
@@ -182,6 +187,15 @@
     }
   }
   
+  public static FSEditLogOp createMkdirOp(String path) {
+    MkdirOp op = MkdirOp.getInstance(new FSEditLogOp.OpInstanceCache())
+      .setPath(path)
+      .setTimestamp(0)
+      .setPermissionStatus(new PermissionStatus(
+              "testuser", "testgroup", FsPermission.getDefault()));
+    return op;
+  }
+  
   /**
    * @return the number of blocks marked safe by safemode, or -1
    * if safemode is not running.
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLog.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLog.java
index f11d2a8..16dd099 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLog.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLog.java
@@ -1220,7 +1220,7 @@
       elfos.create();
       elfos.writeRaw(garbage, 0, garbage.length);
       elfos.setReadyToFlush();
-      elfos.flushAndSync();
+      elfos.flushAndSync(true);
       elfos.close();
       elfos = null;
       file = new File(TEST_LOG_NAME);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLogFileOutputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLogFileOutputStream.java
index 22ab02d..24446d6 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLogFileOutputStream.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestEditLogFileOutputStream.java
@@ -55,7 +55,7 @@
   static void flushAndCheckLength(EditLogFileOutputStream elos,
       long expectedLength) throws IOException {
     elos.setReadyToFlush();
-    elos.flushAndSync();
+    elos.flushAndSync(true);
     assertEquals(expectedLength, elos.getFile().length());
   }
   
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestNameNodeRecovery.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestNameNodeRecovery.java
index 23fd3b5..a8dac57 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestNameNodeRecovery.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestNameNodeRecovery.java
@@ -74,7 +74,7 @@
 
       elts.addTransactionsToLog(elfos, cache);
       elfos.setReadyToFlush();
-      elfos.flushAndSync();
+      elfos.flushAndSync(true);
       elfos.close();
       elfos = null;
       file = new File(TEST_LOG_NAME);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestInitializeSharedEdits.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestInitializeSharedEdits.java
index 47182d2..b534c03 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestInitializeSharedEdits.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestInitializeSharedEdits.java
@@ -166,13 +166,13 @@
   }
   
   @Test
-  public void testDontOverWriteExistingDir() {
+  public void testDontOverWriteExistingDir() throws IOException {
     assertFalse(NameNode.initializeSharedEdits(conf, false));
     assertTrue(NameNode.initializeSharedEdits(conf, false));
   }
   
   @Test
-  public void testInitializeSharedEditsConfiguresGenericConfKeys() {
+  public void testInitializeSharedEditsConfiguresGenericConfKeys() throws IOException {
     Configuration conf = new Configuration();
     conf.set(DFSConfigKeys.DFS_NAMESERVICES, "ns1");
     conf.set(DFSUtil.addKeySuffixes(DFSConfigKeys.DFS_HA_NAMENODES_KEY_PREFIX,
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestBestEffortLongFile.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestBestEffortLongFile.java
new file mode 100644
index 0000000..c57dc970
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestBestEffortLongFile.java
@@ -0,0 +1,86 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.util;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Random;
+
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.io.IOUtils;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class TestBestEffortLongFile {
+
+  private static final File FILE = new File(MiniDFSCluster.getBaseDirectory() +
+      File.separatorChar + "TestBestEffortLongFile");
+
+  @Before
+  public void cleanup() {
+    if (FILE.exists()) {
+      assertTrue(FILE.delete());
+    }
+    FILE.getParentFile().mkdirs();
+  }
+  
+  @Test
+  public void testGetSet() throws IOException {
+    BestEffortLongFile f = new BestEffortLongFile(FILE, 12345L);
+    try {
+      // Before the file exists, should return default.
+      assertEquals(12345L, f.get());
+      
+      // And first access should open it.
+      assertTrue(FILE.exists());
+  
+      Random r = new Random();
+      for (int i = 0; i < 100; i++) {
+        long newVal = r.nextLong();
+        // Changing the value should be reflected in the next get() call.
+        f.set(newVal);
+        assertEquals(newVal, f.get());
+        
+        // And should be reflected in a new instance (ie it actually got
+        // written to the file)
+        BestEffortLongFile f2 = new BestEffortLongFile(FILE, 999L);
+        try {
+          assertEquals(newVal, f2.get());
+        } finally {
+          IOUtils.closeStream(f2);
+        }
+      }
+    } finally {
+      IOUtils.closeStream(f);
+    }
+  }
+  
+  @Test
+  public void testTruncatedFileReturnsDefault() throws IOException {
+    assertTrue(FILE.createNewFile());
+    assertEquals(0, FILE.length());
+    BestEffortLongFile f = new BestEffortLongFile(FILE, 12345L);
+    try {
+      assertEquals(12345L, f.get());
+    } finally {
+      f.close();
+    }
+  }
+}
diff --git a/hadoop-project/src/site/site.xml b/hadoop-project/src/site/site.xml
index f449b5d..ae2ab37 100644
--- a/hadoop-project/src/site/site.xml
+++ b/hadoop-project/src/site/site.xml
@@ -54,7 +54,8 @@
     </menu>
     
     <menu name="HDFS" inherit="top">
-      <item name="High Availability" href="hadoop-yarn/hadoop-yarn-site/HDFSHighAvailability.html"/>
+      <item name="High Availability With QJM" href="hadoop-yarn/hadoop-yarn-site/HDFSHighAvailabilityWithQJM.html"/>
+      <item name="High Availability With NFS" href="hadoop-yarn/hadoop-yarn-site/HDFSHighAvailabilityWithNFS.html"/>
       <item name="Federation" href="hadoop-yarn/hadoop-yarn-site/Federation.html"/>
       <item name="WebHDFS REST API" href="hadoop-yarn/hadoop-yarn-site/WebHDFS.html"/>
       <item name="HttpFS Gateway" href="hadoop-hdfs-httpfs/index.html"/>
diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailability.apt.vm b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailabilityWithNFS.apt.vm
similarity index 95%
rename from hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailability.apt.vm
rename to hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailabilityWithNFS.apt.vm
index 7e7cb66..efa3f93 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailability.apt.vm
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailabilityWithNFS.apt.vm
@@ -25,12 +25,21 @@
 * {Purpose}
 
   This guide provides an overview of the HDFS High Availability (HA) feature and
-  how to configure and manage an HA HDFS cluster.
+  how to configure and manage an HA HDFS cluster, using NFS for the shared
+  storage required by the NameNodes.
  
   This document assumes that the reader has a general understanding of
   general components and node types in an HDFS cluster. Please refer to the
   HDFS Architecture guide for details.
 
+* {Note: Using the Quorum Journal Manager or Conventional Shared Storage}
+
+  This guide discusses how to configure and use HDFS HA using a shared NFS
+  directory to share edit logs between the Active and Standby NameNodes. For
+  information on how to configure HDFS HA using the Quorum Journal Manager
+  instead of NFS, please see {{{./HDFSHighAvailabilityWithQJM.html}this
+  alternative guide.}}
+
 * {Background}
 
   Prior to Hadoop 2.0.0, the NameNode was a single point of failure (SPOF) in
@@ -297,7 +306,7 @@
 </property>
 <property>
   <name>dfs.ha.fencing.ssh.connect-timeout</name>
-  <value>
+  <value>30000</value>
 </property>
 ---
 
@@ -375,17 +384,22 @@
 ** Deployment details
 
   After all of the necessary configuration options have been set, one must
-  initially synchronize the two HA NameNodes' on-disk metadata. If you are
-  setting up a fresh HDFS cluster, you should first run the format command (<hdfs
-  namenode -format>) on one of NameNodes. If you have already formatted the
-  NameNode, or are converting a non-HA-enabled cluster to be HA-enabled, you
-  should now copy over the contents of your NameNode metadata directories to
-  the other, unformatted NameNode using <scp> or a similar utility. The location
-  of the directories containing the NameNode metadata are configured via the
-  configuration options <<dfs.namenode.name.dir>> and/or
-  <<dfs.namenode.edits.dir>>. At this time, you should also ensure that the
-  shared edits dir (as configured by <<dfs.namenode.shared.edits.dir>>) includes
-  all recent edits files which are in your NameNode metadata directories.
+  initially synchronize the two HA NameNodes' on-disk metadata.
+
+    * If you are setting up a fresh HDFS cluster, you should first run the format
+    command (<hdfs namenode -format>) on one of NameNodes.
+  
+    * If you have already formatted the NameNode, or are converting a
+    non-HA-enabled cluster to be HA-enabled, you should now copy over the
+    contents of your NameNode metadata directories to the other, unformatted
+    NameNode by running the command "<hdfs namenode -bootstrapStandby>" on the
+    unformatted NameNode. Running this command will also ensure that the shared
+    edits directory (as configured by <<dfs.namenode.shared.edits.dir>>) contains
+    sufficient edits transactions to be able to start both NameNodes.
+  
+    * If you are converting a non-HA NameNode to be HA, you should run the
+    command "<hdfs -initializeSharedEdits>", which will initialize the shared
+    edits directory with the edits data from the local NameNode edits directories.
 
   At this point you may start both of your HA NameNodes as you normally would
   start a NameNode.
@@ -863,4 +877,4 @@
 
       3) Auto-Recovery of storage node failures. Work inprogress 
       {{{https://issues.apache.org/jira/browse/BOOKKEEPER-237 }BOOKKEEPER-237}}.
-         Currently we have the tools to manually recover the data from failed storage nodes.
\ No newline at end of file
+         Currently we have the tools to manually recover the data from failed storage nodes.
diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailability.apt.vm b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailabilityWithQJM.apt.vm
similarity index 72%
copy from hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailability.apt.vm
copy to hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailabilityWithQJM.apt.vm
index 7e7cb66..2aefc35 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailability.apt.vm
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/apt/HDFSHighAvailabilityWithQJM.apt.vm
@@ -16,7 +16,7 @@
   ---
   ${maven.build.timestamp}
 
-HDFS High Availability
+HDFS High Availability Using the Quorum Journal Manager
 
   \[ {{{./index.html}Go Back}} \]
 
@@ -24,13 +24,22 @@
 
 * {Purpose}
 
-  This guide provides an overview of the HDFS High Availability (HA) feature and
-  how to configure and manage an HA HDFS cluster.
+  This guide provides an overview of the HDFS High Availability (HA) feature
+  and how to configure and manage an HA HDFS cluster, using the Quorum Journal
+  Manager (QJM) feature.
  
   This document assumes that the reader has a general understanding of
   general components and node types in an HDFS cluster. Please refer to the
   HDFS Architecture guide for details.
 
+* {Note: Using the Quorum Journal Manager or Conventional Shared Storage}
+
+  This guide discusses how to configure and use HDFS HA using the Quorum
+  Journal Manager (QJM) to share edit logs between the Active and Standby
+  NameNodes. For information on how to configure HDFS HA using NFS for shared
+  storage instead of the QJM, please see
+  {{{./HDFSHighAvailabilityWithNFS.html}this alternative guide.}}
+
 * {Background}
 
   Prior to Hadoop 2.0.0, the NameNode was a single point of failure (SPOF) in
@@ -62,17 +71,15 @@
   necessary.
   
   In order for the Standby node to keep its state synchronized with the Active
-  node, the current implementation requires that the two nodes both have access
-  to a directory on a shared storage device (eg an NFS mount from a NAS). This
-  restriction will likely be relaxed in future versions.
-
-  When any namespace modification is performed by the Active node, it durably
-  logs a record of the modification to an edit log file stored in the shared
-  directory.  The Standby node is constantly watching this directory for edits,
-  and as it sees the edits, it applies them to its own namespace. In the event of
-  a failover, the Standby will ensure that it has read all of the edits from the
-  shared storage before promoting itself to the Active state. This ensures that
-  the namespace state is fully synchronized before a failover occurs.
+  node, both nodes communicate with a group of separate daemons called
+  "JournalNodes" (JNs). When any namespace modification is performed by the
+  Active node, it durably logs a record of the modification to a majority of
+  these JNs. The Standby node is capable of reading the edits from the JNs, and
+  is constantly watching them for changes to the edit log. As the Standby Node
+  sees the edits, it applies them to its own namespace. In the event of a
+  failover, the Standby will ensure that it has read all of the edits from the
+  JounalNodes before promoting itself to the Active state. This ensures that the
+  namespace state is fully synchronized before a failover occurs.
   
   In order to provide a fast failover, it is also necessary that the Standby node
   have up-to-date information regarding the location of blocks in the cluster.
@@ -83,12 +90,11 @@
   NameNodes be Active at a time. Otherwise, the namespace state would quickly
   diverge between the two, risking data loss or other incorrect results.  In
   order to ensure this property and prevent the so-called "split-brain scenario,"
-  the administrator must configure at least one <fencing method> for the shared
-  storage. During a failover, if it cannot be verified that the previous Active
-  node has relinquished its Active state, the fencing process is responsible for
-  cutting off the previous Active's access to the shared edits storage. This
-  prevents it from making any further edits to the namespace, allowing the new
-  Active to safely proceed with failover.
+  the JournalNodes will only ever allow a single NameNode to be a writer at a
+  time. During a failover, the NameNode which is to become active will simply
+  take over the role of writing to the JournalNodes, which will effectively
+  prevent the other NameNode from continuing in the Active state, allowing the
+  new Active to safely proceed with failover.
 
 * {Hardware resources}
 
@@ -98,17 +104,17 @@
     Standby NameNodes should have equivalent hardware to each other, and
     equivalent hardware to what would be used in a non-HA cluster.
 
-    * <<Shared storage>> - you will need to have a shared directory which both
-    NameNode machines can have read/write access to. Typically this is a remote
-    filer which supports NFS and is mounted on each of the NameNode machines.
-    Currently only a single shared edits directory is supported. Thus, the
-    availability of the system is limited by the availability of this shared edits
-    directory, and therefore in order to remove all single points of failure there
-    needs to be redundancy for the shared edits directory. Specifically, multiple
-    network paths to the storage, and redundancy in the storage itself (disk,
-    network, and power). Beacuse of this, it is recommended that the shared storage
-    server be a high-quality dedicated NAS appliance rather than a simple Linux
-    server.
+    * <<JournalNode machines>> - the machines on which you run the JournalNodes.
+    The JournalNode daemon is relatively lightweight, so these daemons may
+    reasonably be collocated on machines with other Hadoop daemons, for example
+    NameNodes, the JobTracker, or the YARN ResourceManager. <<Note:>> There
+    must be at least 3 JournalNode daemons, since edit log modifications must be
+    written to a majority of JNs. This will allow the system to tolerate the
+    failure of a single machine. You may also run more than 3 JournalNodes, but
+    in order to actually increase the number of failures the system can tolerate,
+    you should run an odd number of JNs, (i.e. 3, 5, 7, etc.). Note that when
+    running with N JournalNodes, the system can tolerate at most (N - 1) / 2
+    failures and continue to function normally.
   
   Note that, in an HA cluster, the Standby NameNode also performs checkpoints of
   the namespace state, and thus it is not necessary to run a Secondary NameNode,
@@ -221,19 +227,28 @@
     <<Note:>> If you have Hadoop's security features enabled, you should also set
     the <https-address> similarly for each NameNode.
 
-  * <<dfs.namenode.shared.edits.dir>> - the location of the shared storage directory
+  * <<dfs.namenode.shared.edits.dir>> - the URI which identifies the group of JNs where the NameNodes will write/read edits
 
-    This is where one configures the path to the remote shared edits directory
-    which the Standby NameNode uses to stay up-to-date with all the file system
-    changes the Active NameNode makes. <<You should only configure one of these
-    directories.>> This directory should be mounted r/w on both NameNode machines.
-    The value of this setting should be the absolute path to this directory on the
-    NameNode machines. For example:
+    This is where one configures the addresses of the JournalNodes which provide
+    the shared edits storage, written to by the Active nameNode and read by the
+    Standby NameNode to stay up-to-date with all the file system changes the Active
+    NameNode makes. Though you must specify several JournalNode addresses,
+    <<you should only configure one of these URIs.>> The URI should be of the form:
+    "qjournal://<host1:port1>;<host2:port2>;<host3:port3>/<journalId>". The Journal
+    ID is a unique identifier for this nameservice, which allows a single set of
+    JournalNodes to provide storage for multiple federated namesystems. Though not
+    a requirement, it's a good idea to reuse the nameservice ID for the journal
+    identifier.
+
+    For example, if the JournalNodes for this cluster were running on the
+    machines "node1.example.com", "node2.example.com", and "node3.example.com" and
+    the nameservice ID were "mycluster", you would use the following as the value
+    for this setting (the default port for the JournalNode is 8485):
 
 ----
 <property>
   <name>dfs.namenode.shared.edits.dir</name>
-  <value>file:///mnt/filer1/dfs/ha-name-dir-shared</value>
+  <value>qjournal://node1.example.com:8485;node2.example.com:8485;node3.example.com:8485/mycluster</value>
 </property>
 ----
 
@@ -254,15 +269,26 @@
 
   * <<dfs.ha.fencing.methods>> - a list of scripts or Java classes which will be used to fence the Active NameNode during a failover
 
-    It is critical for correctness of the system that only one NameNode be in the
-    Active state at any given time. Thus, during a failover, we first ensure that
-    the Active NameNode is either in the Standby state, or the process has
-    terminated, before transitioning the other NameNode to the Active state. In
-    order to do this, you must configure at least one <<fencing method.>> These are
-    configured as a carriage-return-separated list, which will be attempted in order
-    until one indicates that fencing has succeeded. There are two methods which
-    ship with Hadoop: <shell> and <sshfence>. For information on implementing
-    your own custom fencing method, see the <org.apache.hadoop.ha.NodeFencer> class.
+    It is desirable for correctness of the system that only one NameNode be in
+    the Active state at any given time. <<Importantly, when using the Quorum
+    Journal Manager, only one NameNode will ever be allowed to write to the
+    JournalNodes, so there is no potential for corrupting the file system metadata
+    from a split-brain scenario.>> However, when a failover occurs, it is still
+    possible that the previous Active NameNode could serve read requests to
+    clients, which may be out of date until that NameNode shuts down when trying to
+    write to the JournalNodes. For this reason, it is still desirable to configure
+    some fencing methods even when using the Quorum Journal Manager. However, to
+    improve the availability of the system in the event the fencing mechanisms
+    fail, it is advisable to configure a fencing method which is guaranteed to
+    return success as the last fencing method in the list. Note that if you choose
+    to use no actual fencing methods, you still must configure something for this
+    setting, for example "<<<shell(/bin/true)>>>".
+
+    The fencing methods used during a failover are configured as a
+    carriage-return-separated list, which will be attempted in order until one
+    indicates that fencing has succeeded. There are two methods which ship with
+    Hadoop: <shell> and <sshfence>. For information on implementing your own custom
+    fencing method, see the <org.apache.hadoop.ha.NodeFencer> class.
 
     * <<sshfence>> - SSH to the Active NameNode and kill the process
 
@@ -297,7 +323,7 @@
 </property>
 <property>
   <name>dfs.ha.fencing.ssh.connect-timeout</name>
-  <value>
+  <value>30000</value>
 </property>
 ---
 
@@ -372,20 +398,46 @@
 </property>
 ---
 
+
+  * <<dfs.journalnode.edits.dir>> - the path where the JournalNode daemon will store its local state
+
+    This is the absolute path on the JournalNode machines where the edits and
+    other local state used by the JNs will be stored. You may only use a single
+    path for this configuration. Redundancy for this data is provided by running
+    multiple separate JournalNodes, or by configuring this directory on a
+    locally-attached RAID array. For example:
+
+---
+<property>
+  <name>dfs.journalnode.edits.dir</name>
+  <value>/path/to/journal/node/local/data</value>
+</property>
+---
+
 ** Deployment details
 
-  After all of the necessary configuration options have been set, one must
-  initially synchronize the two HA NameNodes' on-disk metadata. If you are
-  setting up a fresh HDFS cluster, you should first run the format command (<hdfs
-  namenode -format>) on one of NameNodes. If you have already formatted the
-  NameNode, or are converting a non-HA-enabled cluster to be HA-enabled, you
-  should now copy over the contents of your NameNode metadata directories to
-  the other, unformatted NameNode using <scp> or a similar utility. The location
-  of the directories containing the NameNode metadata are configured via the
-  configuration options <<dfs.namenode.name.dir>> and/or
-  <<dfs.namenode.edits.dir>>. At this time, you should also ensure that the
-  shared edits dir (as configured by <<dfs.namenode.shared.edits.dir>>) includes
-  all recent edits files which are in your NameNode metadata directories.
+  After all of the necessary configuration options have been set, you must
+  start the JournalNode daemons on the set of machines where they will run. This
+  can be done by running the command "<hdfs-daemon.sh journalnode>" and waiting
+  for the daemon to start on each of the relevant machines.
+
+  Once the JournalNodes have been started, one must initially synchronize the
+  two HA NameNodes' on-disk metadata.
+
+    * If you are setting up a fresh HDFS cluster, you should first run the format
+    command (<hdfs namenode -format>) on one of NameNodes.
+  
+    * If you have already formatted the NameNode, or are converting a
+    non-HA-enabled cluster to be HA-enabled, you should now copy over the
+    contents of your NameNode metadata directories to the other, unformatted
+    NameNode by running the command "<hdfs namenode -bootstrapStandby>" on the
+    unformatted NameNode. Running this command will also ensure that the
+    JournalNodes (as configured by <<dfs.namenode.shared.edits.dir>>) contain
+    sufficient edits transactions to be able to start both NameNodes.
+  
+    * If you are converting a non-HA NameNode to be HA, you should run the
+    command "<hdfs -initializeSharedEdits>", which will initialize the
+    JournalNodes with the edits data from the local NameNode edits directories.
 
   At this point you may start both of your HA NameNodes as you normally would
   start a NameNode.
@@ -713,154 +765,3 @@
   Even if automatic failover is configured, you may initiate a manual failover
   using the same <<<hdfs haadmin>>> command. It will perform a coordinated
   failover.
-
- 
-* BookKeeper as a Shared storage (EXPERIMENTAL)
-
-   One option for shared storage for the NameNode is BookKeeper. 
-  BookKeeper achieves high availability and strong durability guarantees by replicating
-  edit log entries across multiple storage nodes. The edit log can be striped across 
-  the storage nodes for high performance. Fencing is supported in the protocol, i.e, 
-  BookKeeper will not allow two writers to write the single edit log.
-
-  The meta data for BookKeeper is stored in ZooKeeper.
-  In current HA architecture, a Zookeeper cluster is required for ZKFC. The same cluster can be
-  for BookKeeper metadata.
-
-  For more details on building a BookKeeper cluster, please refer to the 
-   {{{http://zookeeper.apache.org/bookkeeper/docs/trunk/bookkeeperConfig.html }BookKeeper documentation}}
-
- The BookKeeperJournalManager is an implementation of the HDFS JournalManager interface, which allows custom write ahead logging implementations to be plugged into the HDFS NameNode.
- 
- **<<BookKeeper Journal Manager>>
-
-   To use BookKeeperJournalManager, add the following to hdfs-site.xml.
-
-----
-    <property>
-      <name>dfs.namenode.shared.edits.dir</name>
-      <value>bookkeeper://zk1:2181;zk2:2181;zk3:2181/hdfsjournal</value>
-    </property>
-
-    <property>
-      <name>dfs.namenode.edits.journal-plugin.bookkeeper</name>
-      <value>org.apache.hadoop.contrib.bkjournal.BookKeeperJournalManager</value>
-    </property>
-----
-
-   The URI format for bookkeeper is <<<bookkeeper://[zkEnsemble]/[rootZnode]
-   [zookkeeper ensemble]>>> is a list of semi-colon separated, zookeeper host:port
-   pairs. In the example above there are 3 servers, in the ensemble,
-   zk1, zk2 & zk3, each one listening on port 2181.
-
-   <<<[root znode]>>> is the path of the zookeeper znode, under which the edit log
-   information will be stored.
-
-   The class specified for the journal-plugin must be available in the NameNode's
-   classpath. We explain how to generate a jar file with the journal manager and
-   its dependencies, and how to put it into the classpath below.
-
- *** <<More configuration options>> 
-
-     * <<dfs.namenode.bookkeeperjournal.output-buffer-size>> - 
-       Number of bytes a bookkeeper journal stream will buffer before
-       forcing a flush. Default is 1024.
-     
-----
-       <property>
-         <name>dfs.namenode.bookkeeperjournal.output-buffer-size</name>
-         <value>1024</value>
-       </property>
-----
-
-     * <<dfs.namenode.bookkeeperjournal.ensemble-size>> - 
-       Number of bookkeeper servers in edit log ensembles. This
-       is the number of bookkeeper servers which need to be available
-       for the edit log to be writable. Default is 3.
-
-----
-       <property>
-         <name>dfs.namenode.bookkeeperjournal.ensemble-size</name>
-         <value>3</value>
-       </property>
-----
-
-     * <<dfs.namenode.bookkeeperjournal.quorum-size>> - 
-       Number of bookkeeper servers in the write quorum. This is the
-       number of bookkeeper servers which must have acknowledged the
-       write of an entry before it is considered written. Default is 2.
-
-----
-       <property>
-         <name>dfs.namenode.bookkeeperjournal.quorum-size</name>
-         <value>2</value>
-       </property>
-----
-
-     * <<dfs.namenode.bookkeeperjournal.digestPw>> - 
-       Password to use when creating edit log segments.
-
-----
-       <property>
-        <name>dfs.namenode.bookkeeperjournal.digestPw</name>
-        <value>myPassword</value>
-       </property>
-----
-
-     * <<dfs.namenode.bookkeeperjournal.zk.session.timeout>> - 
-       Session timeout for Zookeeper client from BookKeeper Journal Manager.
-       Hadoop recommends that this value should be less than the ZKFC 
-       session timeout value. Default value is 3000.
-
-----
-       <property>
-         <name>dfs.namenode.bookkeeperjournal.zk.session.timeout</name>
-         <value>3000</value>
-       </property>
-----
-
- *** <<Building BookKeeper Journal Manager plugin jar>>
-
-     To generate the distribution packages for BK journal, do the
-     following.
-
-     $ mvn clean package -Pdist
-
-     This will generate a jar with the BookKeeperJournalManager, all the dependencies
-     needed by the journal manager,
-     hadoop-hdfs/src/contrib/bkjournal/target/hadoop-hdfs-bkjournal-<VERSION>.jar
-
-     Note that the -Pdist part of the build command is important, as otherwise
-     the dependencies would not be packaged in the jar. The dependencies included in
-     the jar are {{{http://maven.apache.org/plugins/maven-shade-plugin/}shaded}} to
-     avoid conflicts with other dependencies of the NameNode.
-
- *** <<Putting the BookKeeperJournalManager in the NameNode classpath>>
-
-    To run a HDFS namenode using BookKeeper as a backend, copy the bkjournal
-    jar, generated above, into the lib directory of hdfs. In the standard 
-    distribution of HDFS, this is at $HADOOP_HDFS_HOME/share/hadoop/hdfs/lib/
-
-    cp hadoop-hdfs/src/contrib/bkjournal/target/hadoop-hdfs-bkjournal-<VERSION>.jar $HADOOP_HDFS_HOME/share/hadoop/hdfs/lib/
-
- *** <<Current limitations>> 
-
-      1) NameNode format command will not format the BookKeeper data automatically. 
-         We have to clean the data manually from BookKeeper cluster 
-         and create the /ledgers/available path in Zookeeper. 
-----
-$ zkCli.sh create /ledgers 0
-$ zkCli.sh create /ledgers/available 0
-----
-         Note:
-          bookkeeper://zk1:2181;zk2:2181;zk3:2181/hdfsjournal
-          The final part /hdfsjournal specifies the znode in zookeeper where
-          ledger metadata will be stored. Administrators may set this to anything
-          they wish.
-
-      2) Security in BookKeeper. BookKeeper does not support SASL nor SSL for
-         connections between the NameNode and BookKeeper storage nodes.
-
-      3) Auto-Recovery of storage node failures. Work inprogress 
-      {{{https://issues.apache.org/jira/browse/BOOKKEEPER-237 }BOOKKEEPER-237}}.
-         Currently we have the tools to manually recover the data from failed storage nodes.
\ No newline at end of file