The store module allows you to control how index data is stored and accessed on disk.

File system storage typesedit

There are different file system implementations or storage types. By default, Elasticsearch will pick the best implementation based on the operating environment.

This can be overridden for all indices by adding this to the config/elasticsearch.yml file: niofs

It is a static setting that can be set on a per-index basis at index creation time:

PUT /my_index
  "settings": {
    "": "niofs"

This is an expert-only setting and may be removed in the future.

The following sections lists all the different storage types supported.

Default file system implementation. This will pick the best implementation depending on the operating environment, which is currently hybridfs on all supported systems but is subject to change.
The Simple FS type is a straightforward implementation of file system storage (maps to Lucene SimpleFsDirectory) using a random access file. This implementation has poor concurrent performance (multiple threads will bottleneck). It is usually better to use the niofs when you need index persistence.
The NIO FS type stores the shard index on the file system (maps to Lucene NIOFSDirectory) using NIO. It allows multiple threads to read from the same file concurrently. It is not recommended on Windows because of a bug in the SUN Java implementation.
The MMap FS type stores the shard index on the file system (maps to Lucene MMapDirectory) by mapping a file into memory (mmap). Memory mapping uses up a portion of the virtual memory address space in your process equal to the size of the file being mapped. Before using this class, be sure you have allowed plenty of virtual address space.
The hybridfs type is a hybrid of niofs and mmapfs, which chooses the best file system type for each type of file based on the read access pattern. Currently only the Lucene term dictionary, norms and doc values files are memory mapped. All other files are opened using Lucene NIOFSDirectory. Similarly to mmapfs be sure you have allowed plenty of virtual address space.

You can restrict the use of the mmapfs and the related hybridfs store type via the setting This is a boolean setting indicating whether or not memory-mapping is allowed. The default is to allow it. This setting is useful, for example, if you are in an environment where you can not control the ability to create a lot of memory maps so you need disable the ability to use memory-mapping.