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They are not mentioned in ES glossary.

What is their relationship to other ES entities (shards / nodes / indexes) ?

Bax
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2 Answers2

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Indices is the plural of index. If you have more than one index you call them indices. http://www.thefreedictionary.com/index

MeiSign
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Indices are equivalent to databases in Relational DBMS. Just like Relational Database has schema, ES index has mapping.

Shards => index is broken into shards (in order to distribute them and scale)

Replicas => copies of the shards (provide reliability if a node is lost)

I hope the following diagram(taken from Rafal Kuc's slides) demonstrates the relationship between ES Cluster, Index, Node and Shards.

ES diagram

Also, there's a nice stackoverflow post Shards and replicas in Elasticsearch by @javanna

Community
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prayagupd
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  • I know what is an index/shard/replica. Just not being a native English speaker messed me up. Thank you all for your minuses. – Bax Nov 08 '13 at 07:55
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    @Bax Im a native english speaker and all this time I thought and index and indice were different things. I'm 32........... LLOOLL – JREAM Apr 03 '17 at 18:40
  • Elastic Search recommends to have replica shards in different nodes , but the diagram shows shards and replica shards in same node, what will happen if your node fails for some reason ? – Shaiju T Aug 11 '17 at 06:27
  • `Shard 1` in Node1 has `Replica shard 1` in Node2. Similarly `R3` for `Shard 3` is on `Node 3` which is what elasticsearch recommends as you said - https://www.elastic.co/guide/en/elasticsearch/guide/current/replica-shards.html – prayagupd Aug 11 '17 at 16:22