Why is the minimum recommended size of disk for control plane nodes 1024 GB when installing OpenShift 4 on Azure?

Solution Verified - Updated

Environment

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

Issue

  • The minimum recommended size of the disk for control plane nodes on Azure is remarkably larger than other platforms.

Resolution

Disclaimer: Links contained herein to external website(s) are provided for convenience only. Red Hat has not reviewed the links and is not responsible for the content or its availability. The inclusion of any link to an external website does not imply endorsement by Red Hat of the website or their entities, products or services. You agree that Red Hat is not responsible or liable for any loss or expenses that may result due to your use of (or reliance on) the external site or content.

While StandardSSD_LRS disks are supported for Red Hat OpenShift clusters in Azure, they are not recommended for production environments as the performance of that kind of disks is not enough for etcd. Refer to What type of disk is supported for OpenShift 4 control plane nodes in Azure for additional information about the disks types supported for control plane in Azure. See also Backend Performance Requirements for OpenShift ETCD.

For OpenShift clusters in Azure, Premium_LRS 1024 GB disks are the minimum necessary for ensuring enough IOPS performance for etcd. Refer to OpenShift 4 performance degradation on Azure for additional information.

The default configuration can be shown in the source code:

Root Cause

In Azure, disk performance is directly related to disk size, and for etcd it is required that the disks used by control plane nodes are at least 1024 GB (1 TB) for ensuring enough IOPS for etcd. Azure Disks from different regions were tested in Azure Disk performance by region.

Diagnostic Steps

Check the osDisk configured for the control plane machines:

$ oc get machines -n openshift-machine-api
[...]
$ oc get machine [control-plane-machine_name] -n openshift-machine-api -o yaml
[...]
      osDisk:
        diskSettings: {}
        diskSizeGB: 512
        managedDisk:
          storageAccountType: Premium_LRS
        osType: Linux
[...]
SBR
Product(s)
Components
Category
Tags

This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.