Mounting separate disk for OpenShift 4 etcd

Solution Verified - Updated

Environment

  • Red Hat OpenShift Container Platform (RHOCP)
    • 4
  • etcd

Issue

  • How to mount a separate disk for etcd on OpenShift control plane nodes.
  • How to mount a separate disk for /var/lib/etcd on OpenShift master nodes.
  • Due to bad etcd disk performance, a separate disk for etcd is needed.
  • Following the recommendations in etcd backend performance requirements for OpenShift, it is needed to configure a separate disk for etcd in our installed cluster.
  • There is a way to separate /var/lib/containers to a different disk: Mounting separate disk for OpenShift 4 container storage. Is it possible to do the same with /var/lib/etcd?
  • Bad etcd performance.

Resolution

Starting with OpenShift 4.6, it is possible to configure an additional disk for etcd during the installation, following the documentation: Disk partitioning.

In recent versions of OpenShift 4, it is possible to move etcd to a different disk following the documentation:

IMPORTANT NOTE: it is not supported to move etcd to a different disk following the documentation when using control plane machine sets (CPMS).

There is an internal RFE-479 to add the ability to configure a separate disk in IPI installations, and also RFE-5214 for creating additional data disk using MachineSet in Azure, but still not implemented.

Root Cause

Some of the most common issues with etcd are caused by slow storage. Separating the /var/lib/etcd to a different and faster disk could help resolving those issues.
For additional information about the etcd requirements, please review etcd backend performance requirements for OpenShift.

While this process can be used to mount additional disks to a RHEL CoreOS node, support is limited to no more than one additional disk/partition. Please see Understanding OpenShift File System Monitoring (eviction conditions) for more information.

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