# Does cluster.routing.allocation.cluster\_concurrent\_rebalance limit the number of reallocation due to a high watermark?

**URL:** https://discuss.elastic.co/t/does-cluster-routing-allocation-cluster-concurrent-rebalance-limit-the-number-of-reallocation-due-to-a-high-watermark/292555
**Category:** Elasticsearch
**Created:** [December 21, 2021, 11:56am UTC](https://discuss.elastic.co/t/does-cluster-routing-allocation-cluster-concurrent-rebalance-limit-the-number-of-reallocation-due-to-a-high-watermark/292555 "2021-12-21T11:56:17Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![alsyia](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/alsyia/32/87334_2.png) [@alsyia](https://discuss.elastic.co/u/alsyia)
#### Post date: [December 21, 2021, 11:56am UTC](https://discuss.elastic.co/t/does-cluster-routing-allocation-cluster-concurrent-rebalance-limit-the-number-of-reallocation-due-to-a-high-watermark/292555/1 "2021-12-21T11:56:17Z")

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Hello,

We had an event this morning were a node reached its high watermark. Elasticsearch decided to move 21 of its shards.  
We didn't modify **cluster.routing.allocation.cluster\_concurrent\_rebalance** , so it should limit the reallocation to two, right? Is this parameter not respected when reallocations are due to a high watermark?

We had **cluster.routing.allocation.node\_concurrent\_recoveries** set to a somewhat high value (20) though, but our understanding is that this specific parameter only happen when recovering, while the move we saw were clearly labelled as a reallocation...

Thanks!

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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 21, 2021, 5:15pm UTC](https://discuss.elastic.co/t/does-cluster-routing-allocation-cluster-concurrent-rebalance-limit-the-number-of-reallocation-due-to-a-high-watermark/292555/2 "2021-12-21T17:15:22Z")

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> [@alsyia](#):
>
> Is this parameter not respected when reallocations are due to a high watermark?

`cluster.routing.allocation.cluster_concurrent_rebalance` only affects rebalance operations, but moving shards due to a disk watermark are different (and higher-priority) so they are not sensitive to this parameter.

> [@alsyia](#):
>
> We had **cluster.routing.allocation.node\_concurrent\_recoveries** set to a somewhat high value (20) though

It's almost always best to leave `cluster.routing.allocation.node_concurrent_recoveries` set to the default of `2`. If you want faster recoveries and your system can handle it then increase `indices.recovery.max_bytes_per_sec` instead.

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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 18, 2022, 5:16pm UTC](https://discuss.elastic.co/t/does-cluster-routing-allocation-cluster-concurrent-rebalance-limit-the-number-of-reallocation-due-to-a-high-watermark/292555/3 "2022-01-18T17:16:01Z")

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