# Reindex from remote very slow

**URL:** <https://discuss.elastic.co/t/reindex-from-remote-very-slow/278497>\
**Category:** Elasticsearch\
**Created:** [July 13, 2021, 7:31am UTC](https://discuss.elastic.co/t/reindex-from-remote-very-slow/278497 "2021-07-13T07:31:52Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![bacquelmore](https://avatars.discourse-cdn.com/v4/letter/b/dc4da7/32.png) [@bacquelmore](https://discuss.elastic.co/u/bacquelmore)\
**Post date:** [July 13, 2021, 7:31am UTC](https://discuss.elastic.co/t/reindex-from-remote-very-slow/278497/1 "2021-07-13T07:31:52Z")

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Hi,

I am trying to reindex from remote an index of ~40Gb, single shard, single node, to an index of 8 shards, 3 nodes. The operation is very slow (now a couple of days) and seems to only progress during specific hours of the day: when querying the reindexing task status, I see that the number of documents copied doesn't change, expect at certain point of the day. I checked the cloudwatch metrics of the master node and saw that indeed, there are periodic peaks of Bandwitdth/Throughput every day, corresponding to when the reindexing task makes some progress:

 ![Screenshot 2021-07-13 at 09.22.17](https://us1.discourse-cdn.com/elastic/original/3X/1/5/155aeb52d71a8e79ae20aff641e06aa5f8caf72c.png)

I guess something else is happening during the rest of the day, but I don't know what/why (merging? syncing between shards/nodes?). I can see that all the 8 shards roughly have the same size (growing slowly).

I've set number of replicas to 0, resfresh interval to -1. Here is the \_stats of the reindex node (the destination): [{ "\_shards" : { "total" : 8, "successful" : 8, "failed" : 0 - Pastebin.com](https://pastebin.com/6wY9Rnea)

The 3 nodes are c5a.large instances (4Gb of RAM), the ES heap size is 2Gb. The disks are GP3 SSD with 10000 IOPS and 500MB/s of throughput. ES version is 7.6.2

I have the following questions:

- What can be the reason of this slow re-indexing? How can I speed it up?
- Is it safe to use the new index instead of the old one while the re-index operation is running? (To write new documents and read current ones)

Thanks a lot for your help!

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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 10, 2021, 7:32am UTC](https://discuss.elastic.co/t/reindex-from-remote-very-slow/278497/2 "2021-08-10T07:32:00Z")

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