# How does Re-index API works?

**URL:** <https://discuss.elastic.co/t/how-does-re-index-api-works/251293>\
**Category:** Elasticsearch\
**Created:** [October 7, 2020, 3:10pm UTC](https://discuss.elastic.co/t/how-does-re-index-api-works/251293 "2020-10-07T15:10:11Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![srbhklkrn](https://avatars.discourse-cdn.com/v4/letter/s/e480ec/32.png) [@srbhklkrn](https://discuss.elastic.co/u/srbhklkrn)\
**Post date:** [October 7, 2020, 3:10pm UTC](https://discuss.elastic.co/t/how-does-re-index-api-works/251293/1 "2020-10-07T15:10:11Z")

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We are in the process of migrating from ES 6.4 to 7.9, and around 3 TB of data. I'm looking into reindex API to start the process and do testing. My question is does reindex API will delete the original indexes? for now, I just want to test the cluster and see if alerting works as we expect.

Also, is there any recommended or documented process on how we move from the old cluster to new?

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**Author:** ![Wolfram\_Haussig](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/wolfram_haussig/32/70528_2.png) [@Wolfram\_Haussig](https://discuss.elastic.co/u/Wolfram_Haussig)\
**Post date:** [October 8, 2020, 5:23am UTC](https://discuss.elastic.co/t/how-does-re-index-api-works/251293/2 "2020-10-08T05:23:46Z")

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Hi,

Reindex only creates new indizes without affecting the original ones.

Did you already have a look at [this](https://www.elastic.co/guide/en/elasticsearch/reference/current/setup-upgrade.html) document? It is recommended to upgrade to 6.8 first, check the migration analyzer(available in 6.8 under management) for problems and after this upgrade to 7.9.

Best regards  
Wolfram

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<div class="post-metadata">

**Author:** ![srbhklkrn](https://avatars.discourse-cdn.com/v4/letter/s/e480ec/32.png) [@srbhklkrn](https://discuss.elastic.co/u/srbhklkrn)\
**Post date:** [October 8, 2020, 1:36pm UTC](https://discuss.elastic.co/t/how-does-re-index-api-works/251293/3 "2020-10-08T13:36:15Z")

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Hi Wolfram,

I'm not doing an in-place upgrade, I have created a new 7.9 cluster and now just need to copy all the indexes.

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**Author:** ![Wolfram\_Haussig](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/wolfram_haussig/32/70528_2.png) [@Wolfram\_Haussig](https://discuss.elastic.co/u/Wolfram_Haussig)\
**Post date:** [October 9, 2020, 6:30am UTC](https://discuss.elastic.co/t/how-does-re-index-api-works/251293/4 "2020-10-09T06:30:25Z")

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Hi,

Sorry, I didn't catch that you created a new cluster. In this case, I think it would be best to do a snapshot of the old system and mount the snapshot repository as readonly in the new system and do a restore from there: [https://www.elastic.co/guide/en/elasticsearch/reference/current/snapshot-restore.html](https://www.elastic.co/guide/en/elasticsearch/reference/current/snapshot-restore.html)

You might still want to reindex the data after migration to convert the 6.x indexes to the 7.x format...

Best regards  
Wolfram

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [November 6, 2020, 6:30am UTC](https://discuss.elastic.co/t/how-does-re-index-api-works/251293/5 "2020-11-06T06:30:31Z")

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