During an upgrade from vSphere 5.0 to vSphere 5.5 we stumbled upon a problem.
We needed to redo the vCenter Server (which isn’t really a problem) but the old cluster had EVC Penryn enabled.
We created a new vCenter Server, created a new Cluster and tried to join a host to it…
No chance… vCenter was telling us that it couldn’t join the host to the cluster with EVC enabled (as the vms where still running).
Ok, so than disable EVC and join the hosts… no issue.
Now enable EVC again…
No chances… some VMs on some servers where using a higher level of CPU Instructions than the EVC level we wanted to enable supported.
So we created a temporary cluster, moved the 2 esx servers with the offending vms into it, by removing them from the vCenter server first as the vms need to be kept running.
Than we set the EVC mode on the original cluster and started migrating the vms from the temp cluster into the EVC enabled cluster.
We only found 2 VMs which we couldn’t migrate as they where using features which weren’t supported on the EVC enabled cluster, one was a MS SQL server.
So we needed to shut them down, migrate them and power them up again.
Yes this isn’t your typical approach on upgrading a vSphere environment, but in the end it did work.