I’ve been asked recently about issues people encounter when trying to enable Enhanced VMotion Compatibility (EVC) processor support and putting ESX/ESXi hosts into those clusters. While I’m not going to go into the details of EVC, what’s important to understand because you are setting the cluster to the lowest common denominator of the CPUs across the hosts in the cluster:
… any hosts that are to be moved into the cluster whether they host virtual machines or not will require you to put them into maintenance mode. Failure to put the host into maintenance mode will throw the following error when you try to move it into an EVC enabled cluster:
The operation is not allowed in the current state.
What you need to do is put the host into maintenance mode first:
Then move the hosts into the new EVC enabled cluster: