// Module included in the following assemblies:
//
// * etcd/etcd-performance.adoc

:_mod-docs-content-type: CONCEPT
[id="etcd-disk-latency_{context}"]
= Effects of disk latency on etcd

[role="_abstract"]
etcd performance depends heavily on disk latency for fsync operations. Validate storage with `fio` before deployment so you avoid instability, failed writes, and service-affecting control plane events.

An etcd cluster is sensitive to disk latencies. To understand the disk latency that is experienced by etcd in your control plane environment, run the `fio` tests or suite.

Ensure that the final report classifies the disk as appropriate for etcd, as shown in the following example:

[source,terminal]
----
...
99th percentile of fsync is 5865472 ns
99th percentile of the fsync is within the recommended threshold: - 20 ms, the disk can be used to host etcd
----

When a high latency disk is used, a message states that the disk is not recommended for etcd, as shown in the following example:

[source,terminal]
----
...
99th percentile of fsync is 15865472 ns
99th percentile of the fsync is greater than the recommended value which is 20 ms, faster disks are recommended to host etcd for better performance
----

When you use cluster deployments that span multiple data centers that are using disks for etcd that do not meet the recommended latency, it increases the chances of service-affecting failures and dramatically reduces the network latency that the control plane can sustain.
