# Add an existing index as a backing index for a data stream

**URL:** <https://discuss.elastic.co/t/add-an-existing-index-as-a-backing-index-for-a-data-stream/353892>\
**Category:** Elasticsearch\
**Created:** [February 22, 2024, 2:25pm UTC](https://discuss.elastic.co/t/add-an-existing-index-as-a-backing-index-for-a-data-stream/353892 "2024-02-22T14:25:00Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![christian.k](https://avatars.discourse-cdn.com/v4/letter/c/87869e/32.png) [@christian.k](https://discuss.elastic.co/u/christian.k)\
**Post date:** [February 22, 2024, 2:25pm UTC](https://discuss.elastic.co/t/add-an-existing-index-as-a-backing-index-for-a-data-stream/353892/1 "2024-02-22T14:25:00Z")

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The documentation for adding an existing index as a backing index for a data stream warns that this is an expert-level API and "can potentially result in improper data stream behavior" (see [Modify data streams API | Elasticsearch Guide [8.12] | Elastic](https://www.elastic.co/guide/en/elasticsearch/reference/current/modify-data-streams-api.html)).

Can anyone explain in what cases this API results in improper data stream behavior?

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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:** [March 21, 2024, 2:25pm UTC](https://discuss.elastic.co/t/add-an-existing-index-as-a-backing-index-for-a-data-stream/353892/2 "2024-03-21T14:25:06Z")

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