IBM
qcow2 files for OCP node storage leads to poor CPU performance
We've observed very high iowait time being consumed by OCP cluster nodes when they are performing high amount of disk IO.
Please update the automation to give the option to use raw block (SCSI LUN or DASD) devices and pass these through to the OCP guest nodes.
More information about implementation can be found here: https://www.redbooks.ibm.com/redbooks/pdfs/sg248463.pdf Chapter 3.6
RH Bug: https://issues.redhat.com/browse/ITIBM-215
Info: https://www.cnblogs.com/popsuper1982/p/3845437.html
Another team uses the unsupported IPI method to deploy their clusters, and are using qcow2. I wonder if applying the pattern in this tuning playbook would be sufficient to avoid the iowait issue, and continue to use qcow2?
https://github.com/ibm-s390-cloud/ocp-kvm-ipi-automation/blob/main/ansible/roles/tuning/tasks/libvirt_optimize_disks.yml
Are there tuning playbooks for these optimizations? https://docs.openshift.com/container-platform/4.13/scalability_and_performance/ibm-z-recommended-host-practices.html