Enhanced vMotion Compatibility

[andvm]

Hi,

If EVC is not set at cluster level, newly powered on VM's will pick up the EVC according to the Host they are placed on (Assuming a Cluster with different Server models)

Keeping in mind above scenario, updating vCenter will enable new EVC modes, do the ESXi Hosts (that support a newer mode) need to be rebooted to show support for the new EVC mode? (If no reboot is needed I think that newly powered ON VMs will be set to a different EVC mode than the ones that were powered on prior the vCenter update.)

Thanks

[Tibmeister]

Without EVC mode enabled, the VMs will pick up the CPU mode that the host can present.  Updating ESXi doesn't change the underlying processor, so no, it wouldn't present the new modes because the CPU is unchanged.

[andvm]

No I meant do the ESXi need to be restarted to start supporting new modes enabled after a vCenter update?

[Tibmeister]

The EVC modes are tied to the host, although supporting new modes is part of vCenter updates, but that does not change the modes that are available to the host because the hardware doesn't change and new modes won't "upgrade" the modes available by the host.

[andvm]

right but say you got a brand new Host added to an old vCenter ex: 6.7 and no EVC mode has been set.

In this case the Host will only start supporting newer modes when vCenter is updated ex: to 7.0U3

So my question is will the Host unlock the new supported EVC modes automatically for newly powered ON VMs or after the Host is rebooted?

Thanks

[Tibmeister]

The new hosts will be added at a basic level for EVC to match the rest of the cluster, as all hosts in a cluster present the same EVC mode.  If it's a new cluster, then you would set the new cluster's EVC mode to the highest supported.  When you upgrade vCenter and new EVC modes are available, then you just bump the cluster to the new mode, and the host will apply that to VMs when they, the VMs, next reboot.  EVC mode is just a construct of masking features from the VM's vCPU, so once the host knows what features to mask/unmask for the given EVC mode, the VM's pick that up when they reboot/power cycle.

Now if you don't have EVC even enabled on the cluster, then this is all moot.

[andvm]

"so once the host knows what features to mask/unmask for the given EVC mode, the VM's pick that up when they reboot/power cycle."

ok think this answered my question, as in when new features unlocked by a VCSA update on a non EVC enabled cluster are supported, any newly powered ON VM will start utilising those features (No Host restart needed). I know enabling EVC is almost always a must but wanted a deeper understanding on what happens in such scenarios.

Actually I believe in such case the new features are picked up by the VM/s on a Power On, believe a VM reboot still keeps same features.