# Clustering data consistency question

**URL:** <https://discuss.elastic.co/t/clustering-data-consistency-question/212165>\
**Category:** Elasticsearch\
**Created:** [December 17, 2019, 1:09pm UTC](https://discuss.elastic.co/t/clustering-data-consistency-question/212165 "2019-12-17T13:09:06Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![asp](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@asp](https://discuss.elastic.co/u/asp)\
**Post date:** [December 17, 2019, 1:09pm UTC](https://discuss.elastic.co/t/clustering-data-consistency-question/212165/1 "2019-12-17T13:09:06Z")

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Hi,

I have a cluster of 3 nodes where each node has all roles (master, data, ingest).  
I use logstash which pushes the data to elasticsearch.

When is the ack sent to logstash? After the data has been replicated or just when it was saved to the ingest node?

Let's say I have node A,B,C. Logstash is sending a bulk index request to A. Is it possible that data is lost, if A crashes after sending the ack to logstash but before the data is replicated to B or C?

Thanks, Andreas

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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:** [December 17, 2019, 1:35pm UTC](https://discuss.elastic.co/t/clustering-data-consistency-question/212165/2 "2019-12-17T13:35:08Z")

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Elasticsearch only acknowledges a write request after all the documents in that request have been durably written to disk on all in-sync shard copies (primaries and replicas). See [the reference manual](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-replication.html#_basic_write_model) for more details.

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<div class="post-metadata">

**Author:** ![asp](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@asp](https://discuss.elastic.co/u/asp)\
**Post date:** [December 17, 2019, 1:41pm UTC](https://discuss.elastic.co/t/clustering-data-consistency-question/212165/3 "2019-12-17T13:41:01Z")

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thanks for the fast reply.

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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:** [January 14, 2020, 1:41pm UTC](https://discuss.elastic.co/t/clustering-data-consistency-question/212165/4 "2020-01-14T13:41:09Z")

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Closed on January 14, 2020, 1:41pm UTC

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