EVC mode disabled / vmotion works?

[Xvor]

We have 2 ESXi clusters within our vSphere setup, vSphere is version 5.5U1, currently latest available build.

Cluster 1 has Intel Xeon E7540 CPUs.

Cluster 2 is brand new and uses recently released Intel Xeon E7-4860 v2 CPUs.

EVC is currently disabled on both clusters.

All systems are listed in the VMware compatibility guide for our current vSphere version.

I expected this setup to be able to vMotion live virtual machines from the old to the new cluster without the use of EVC on either, but I assumed that migrations back to cluster 1 would require cluster 2 to be assigned the appropriate Intel EVC baseline (Nehalem in this case).

As it turns out, I am able to migrate live VMs in both directions without any (so far) apparent issues, with EVC mode disabled on both clusters.

Is this an expected behavior or could it be that ESXi/vCenter is somehow misreading? the CPU compatibilites (maybe because E7-4860v2 are a very recent model) or some other issue like that which could potentially lead into problems with such migrations?

[MKguy · Accepted solution]

I expected this setup to be able to vMotion live virtual machines from the old to the new cluster without the use of EVC on either, but I assumed that migrations back to cluster 1 would require cluster 2 to be assigned the appropriate Intel EVC baseline (Nehalem in this case).

As it turns out, I am able to migrate live VMs in both directions without any (so far) apparent issues, with EVC mode disabled on both clusters.

Is this an expected behavior or could it be that ESXi/vCenter is somehow misreading? the CPU compatibilites (maybe because E7-4860v2 are a very recent model) or some other issue like that which could potentially lead into problems with such migrations?

This is perfectly normal unless you have power-cycled the VM on the newer hosts.

If a VM was powered-on on an old host and is migrated to the new cluster, it doesn't change the current runlevel CPU features of the VM. It will continue to run with the older CPU features on the new host and thus is able to migrate back to the old host again without issues or any additional helpers like EVC.

However, if you now shutdown the migrated VM and power it on again on the new hosts, the virtual hardware will apply the new host's CPU capabilities (or the cluster EVC level, but you didn't apply any) and you won't be able to migrate the VM back to hosts of the old cluster.

[Xvor]

Yep, that's it, I confused myself by the fact that I only rebooted the test VM and didn't properly power-cycle it, so it continued to work with the same CPU feature set.

Thanks.