[[recovery]]
=== Index recovery settings

Peer recovery syncs data from a primary shard to a new or existing shard copy.

Peer recovery automatically occurs when {es}:

* Recreates a shard lost during node failure
* Relocates a shard to another node due to a cluster rebalance or changes to the
<<modules-cluster, shard allocation settings>>

You can view a list of in-progress and completed recoveries using the
<<cat-recovery, cat recovery API>>.

[discrete]
[[recovery-settings]]
==== Recovery settings

`indices.recovery.max_bytes_per_sec`::
(<<cluster-update-settings,Dynamic>>) Limits total inbound and outbound
recovery traffic for each node. Applies to both peer recoveries as well
as snapshot recoveries (i.e., restores from a snapshot). Defaults to `40mb`
unless the node is a dedicated <<cold-tier, cold>> or
<<frozen-tier, frozen>> node, in which case the default relates to the
total memory available to the node:

.Recovery Rate for Cold Nodes
[options="header"]
|======
|total memory         | default value
|<= 4 GB              | 40 MB/s
|> 4 GB and <= 8 GB   | 60 MB/s
|> 8 GB and <= 16 GB  | 90 MB/s
|> 16 GB and <= 32 GB | 125 MB/s
|> 32 GB              | 250 MB/s
|======

+
This limit applies to each node separately. If multiple nodes in a cluster
perform recoveries at the same time, the cluster's total recovery traffic may
exceed this limit.
+
If this limit is too high, ongoing recoveries may consume an excess of bandwidth
and other resources, which can destabilize the cluster.
+
This is a dynamic setting, which means you can set it in each node's
`elasticsearch.yml` config file and you can update it dynamically using the
<<cluster-update-settings,cluster update settings API>>. If you set it
dynamically then the same limit applies on every node in the cluster. If you do
not set it dynamically then you can set a different limit on each node, which is
useful if some of your nodes have better bandwidth than others. For example, if
you are using <<overview-index-lifecycle-management,Index Lifecycle Management>>
then you may be able to give your hot nodes a higher recovery bandwidth limit
than your warm nodes.

[discrete]
==== Expert peer recovery settings
You can use the following _expert_ setting to manage resources for peer
recoveries.

`indices.recovery.max_concurrent_file_chunks`::
(<<cluster-update-settings,Dynamic>>, Expert) Number of file chunk requests
sent in parallel for each recovery. Defaults to `2`.
+
You can increase the value of this setting when the recovery of a single shard
is not reaching the traffic limit set by `indices.recovery.max_bytes_per_sec`.

`indices.recovery.max_concurrent_operations`::
(<<cluster-update-settings,Dynamic>>, Expert) Number of operations sent
in parallel for each recovery. Defaults to `1`.
+
Concurrently replaying operations during recovery can be very resource-intensive
and may interfere with indexing, search, and other activities in your cluster.
Do not increase this setting without carefully verifying that your cluster has
the resources available to handle the extra load that will result.

