hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/VolumeChoosingPolicy.java

/**
 * 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.server.datanode.fsdataset;

import java.io.IOException;
import java.util.List;

import org.apache.hadoop.classification.InterfaceAudience;

/**
 * This interface specifies the policy for choosing volumes to store replicas.
 */
@InterfaceAudience.Private
public interface VolumeChoosingPolicy<V extends FsVolumeSpi> {

  /**
   * Choose a volume to place a replica,
   * given a list of volumes and the replica size sought for storage.
   * 
   * The implementations of this interface must be thread-safe.
   * 
   * @param volumes - a list of available volumes.
   * @param replicaSize - the size of the replica for which a volume is sought.
   * @return the chosen volume.
   * @throws IOException when disks are unavailable or are full.
   */
  public V chooseVolume(List<V> volumes, long replicaSize) throws IOException;
}