Shards
When you create an index, Elasticsearch subdivides your index into multiple Lucene indices that are called shards. The process of this subdividing is called sharding. Shards are automatically managed by Elasticsearch and are in themselves a fully functional and independent index. You can define a number of shards. By default, a shard is being refreshed per second. Elasticsearch thus supports real-time search. Shards are useful when working with large data because when you have a large index, disk capacity of a single node may not be sufficient or may be too slow to serve search requests. Shards solve such, and similar, problems and allow you to horizontally scale your content volume.
