# Clarifying the difference between Active shards and in-sync copies

**URL:** <https://discuss.elastic.co/t/clarifying-the-difference-between-active-shards-and-in-sync-copies/238716>\
**Category:** Elasticsearch\
**Created:** [June 25, 2020, 3:51pm UTC](https://discuss.elastic.co/t/clarifying-the-difference-between-active-shards-and-in-sync-copies/238716 "2020-06-25T15:51:05Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![paulcarey](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/paulcarey/32/34624_2.png) [@paulcarey](https://discuss.elastic.co/u/paulcarey)\
**Post date:** [June 25, 2020, 3:51pm UTC](https://discuss.elastic.co/t/clarifying-the-difference-between-active-shards-and-in-sync-copies/238716/1 "2020-06-25T15:51:05Z")

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Hi

The [replication docs](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-replication.html) state

> a single in-sync copy is sufficient to serve read requests

and then, when describing the read model, the same doc states that the basic flow

> Select[s] an active copy of each relevant shard

This suggests that _in-sync copies_ and _active copies_ are the same thing.

But this [blog post](https://www.elastic.co/blog/tracking-in-sync-shard-copies) states

> one of the active replicas, which is also in the in-sync set

which clearly implies that there is a difference between the two.

Confusing matters (for me at least) is the `wait_for_active_shards` param on the [Index API](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-index_.html), which makes no reference to in-sync copies.

Are _active copies_ and _in-sync copies_ the same thing? If not, could you please clarify the difference?

Many thanks

Paul

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**Author:** ![paulcarey](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/paulcarey/32/34624_2.png) [@paulcarey](https://discuss.elastic.co/u/paulcarey)\
**Post date:** [July 15, 2020, 8:42am UTC](https://discuss.elastic.co/t/clarifying-the-difference-between-active-shards-and-in-sync-copies/238716/2 "2020-07-15T08:42:57Z")

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ES support confirmed that they are effectively the same; I think I mis-parsed the quote from the blog post above. However, it is possible that a shard could be _in-sync_ but not _active_ e.g. when a green index has been closed.

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**Author:** ![DavidTurner](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/davidturner/32/22453_2.png) [@DavidTurner](https://discuss.elastic.co/u/DavidTurner)\
**Post date:** [July 15, 2020, 9:06am UTC](https://discuss.elastic.co/t/clarifying-the-difference-between-active-shards-and-in-sync-copies/238716/3 "2020-07-15T09:06:18Z")

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A shard copy can also be in-sync but not active if it's unassigned (e.g. the node holding it has shut down) but nothing has been written to that shard since the last time that copy was active. The converse is not possible, however: all active shards are necessarily in-sync.

> a single in-sync copy is sufficient to serve read requests

I think that's wrong, the copy has to be _active_ to serve read requests. If it's closed or unassigned then it obviously can't serve searches, even if it's still in-sync.

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [August 12, 2020, 9:06am UTC](https://discuss.elastic.co/t/clarifying-the-difference-between-active-shards-and-in-sync-copies/238716/4 "2020-08-12T09:06:19Z")

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