Document URL: https://docs.openshift.com/container-platform/4.9/virt/install/preparing-cluster-for-virt.html

Section Number and Name:

Describe the issue: No parapgraph to describe how to calculcate the required spare memory in the cluster in order to enable a certain number of concurrent migrations

Suggestions for improvement: A paragraph describing the relevance of migrations i.e.it's important to ensure there is enough network bandwidth and to use shared storage to enable fast migrations, as this is commonly used to ensure proper cluster upgrades. Further: There must be enough free memory on nodes, to be able to act as a live migration target for VMs. While the system is limitting concurrent live migrations per cluster by default to 5 (link to https://docs.openshift.com/container-platform/4.9/virt/live_migration/virt-live-migration-limits.html) the number of live migrations is further limit by the availability of free memory on nodes. An admin needs to ensure that there will always be enough memory on the cluster to live migrate at least one VM at a time, or at best more. The exact size of the required free memory depends on the sze of the VMs.
Baseline can be: Minimum required free memory: Sum of memory of 5 largest VMs on the cluster.

Additional information: