Guaranteed memory requirements for OpenShift on Red Hat Virtualization clusters

When installing an OpenShift on Red Hat Virtualization cluster, the general minimum requirement is to have at least 112 GiB RAM available on the RHV cluster. Some users, especially on development clusters and POCs, take advantage of RHV memory overcommitment features to reach the memory requirements.
Note: Using memory overcommitment on a production OpenShift cluster is not recommended because the Kubernetes scheduler is unaware of the memory overcommitment, and in edge cases this could lead to OOM problems and unexpected behavior, but it is common in development clusters.

The default behavior of the guaranteed memory field for a newly created virtual machine was changed in RHV 4.4.7 as follows:

• On RHV earlier than 4.4.7: The guaranteed memory value is taken directly from the template.

• On RHV 4.4.7: The guaranteed memory is equal to the Virtual Machine memory.

• On RHV later than 4.4.7: The guaranteed memory is equal to memory, but takes into account the cluster memory overcommitment settings.

  For example, if you create a VM with 10 GB memory, and have 150% memory overcommitment set on the cluster level, you will get 10 GB*0.66 = 6.6 GB of guaranteed memory for the VM.

It is important to take this change into account when installing a new OpenShift cluster on a RHV environment while relying on memory overcommitment.
Essentially, that means that on a RHV 4.4.7 cluster you need to have enough physical memory available, or the installation will fail.