# Migration from ES2.1 to ES6.4
**URL:** https://discuss.elastic.co/t/migration-from-es2-1-to-es6-4/152600
**Category:** Elasticsearch
**Created:** [October 16, 2018, 8:20am UTC](https://discuss.elastic.co/t/migration-from-es2-1-to-es6-4/152600 "2018-10-16T08:20:15Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@boeledi01](https://discuss.elastic.co/u/boeledi01)
#### Post date: [October 16, 2018, 8:20am UTC](https://discuss.elastic.co/t/migration-from-es2-1-to-es6-4/152600/1 "2018-10-16T08:20:15Z")
Hi,
I have to migrate from ES2.1 to ES6.4. I have an index with ~450 million documents.
Could anyone give me a hint on how to do it ?
Many thanks
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### Author:  [@spinscale](https://discuss.elastic.co/u/spinscale)
#### Post date: [October 17, 2018, 7:41am UTC](https://discuss.elastic.co/t/migration-from-es2-1-to-es6-4/152600/2 "2018-10-17T07:41:08Z")
Hey,
you cannot directly upgrade to 6.4, as the data cannot be read due to two major version upgrades (2.x to 5.x to 6.x). Also there are breaking changes in between that you need to cater for.
You basically have two possibilities.
1. Upgrading to latest 5.x first, ensure everything works on 5.x, then go to 6.x from there - and of course ensuring all your clients keep working as expected.
2. Running a parallel 6.x cluster and reindex from 2.x into 6.x, either using the reindex API or have some custom tooling doing that. You could run both clusters in parallel and have infrastructure to index into both clusters, and then switch over your consumers one by one to the new cluster.
--Alex
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [November 14, 2018, 7:43am UTC](https://discuss.elastic.co/t/migration-from-es2-1-to-es6-4/152600/3 "2018-11-14T07:43:08Z")
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