= DataDir and DirectoryFactory in SolrConfig
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Where and how Solr stores its indexes are configurable options.

== Specifying a Location for Index Data with the dataDir Parameter

By default, Solr stores its index data in a directory called `/data` under the core's instance directory (`instanceDir`). If you would like to specify a different directory for storing index data, you can configure the `dataDir` in the `core.properties` file for the core, or use the `<dataDir>` parameter in the `solrconfig.xml` file. You can specify another directory either with an absolute path or a pathname relative to the instanceDir of the SolrCore. For example:

[source,xml]
----
<dataDir>/solr/data/${solr.core.name}</dataDir>
----

The `${solr.core.name}` substitution will cause the name of the current core to be substituted, which results in each core's data being kept in a separate subdirectory.

If you are using replication to replicate the Solr index (as described in <<legacy-scaling-and-distribution.adoc#,Legacy Scaling and Distribution>>), then the `<dataDir>` directory should correspond to the index directory used in the replication configuration.

NOTE: If the environment variable `SOLR_DATA_HOME` is defined, or if `solr.data.home` is configured for your DirectoryFactory, or if `solr.xml` contains an
element `<solrDataHome>` then the location of data directory will be `<SOLR_DATA_HOME>/<instance_name>/data`.

== Specifying the DirectoryFactory For Your Index

The default {solr-javadocs}/core/org/apache/solr/core/NRTCachingDirectoryFactory.html[`solr.NRTCachingDirectoryFactory`] is filesystem based, and tries to pick the best implementation for the current JVM and platform. You can force a particular implementation and/or configuration options by specifying {solr-javadocs}/core/org/apache/solr/core/MMapDirectoryFactory.html[`solr.MMapDirectoryFactory`] or {solr-javadocs}/core/org/apache/solr/core/NIOFSDirectoryFactory.html[`solr.NIOFSDirectoryFactory`].

[source,xml]
----
<directoryFactory name="DirectoryFactory"
                  class="solr.MMapDirectoryFactory">
  <bool name="preload">true</bool>
</directoryFactory>
----

The {solr-javadocs}/core/org/apache/solr/core/RAMDirectoryFactory.html[`solr.RAMDirectoryFactory`] is memory based, not persistent, and does not work with replication. Use this DirectoryFactory to store your index in RAM.

[source,xml]
----
<directoryFactory class="org.apache.solr.core.RAMDirectoryFactory"/>
----

[NOTE]
====
If you are using Hadoop and would like to store your indexes in HDFS, you should use the {solr-javadocs}/core/org/apache/solr/core/HdfsDirectoryFactory.html[`solr.HdfsDirectoryFactory`] instead of either of the above implementations. For more details, see the section <<running-solr-on-hdfs.adoc#,Running Solr on HDFS>>.
====