EVC Compatible

[samcatoe]

Hi all,

My system required an update of vCenter from 5.1 to 6.0 u 2. Going to update proved to be a difficult task due to certificate issues. I ended up just building a new vCenter server and disconnecting the hosts and reconnected the hosts to the new vCenter.

Everything worked perfectly, until I went to go vMotion a VM and then an error popped up.. EVC Compatibility was not enabled and the CPUs on the hosts were different. I had wrongly (so wrongly) assumed they were the same CPU.

Either way, I need to turn it back on to vMotion. Everything I've read states it requires a shut down of the machines, but the if you select the same EVC Compatibility level as the old vCenter, it shows no errors ("Compatibility succeeded").

I did not hit "ok" to change the EVC Compatibility of the cluster because I wasn't sure how the servers would react (since everything I read states this requires the servers to be turned off). Because I connected the hosts into a cluster with EVC disabled while the VMs were still online, did they stay in this mode? Would I see any negative affects by hitting ok since it is not returning any errors when I go to select EVC Compatibility at the same level it was at before?

This is a production system, and like all of us, my biggest fear is to bring down production machines. Normally I would just click ok to see what happens, especially since it seems like vCenter is telling me it's fine, but I'd like to know if this is accurate. Thank you!!

[dineshgoundar · Accepted solution]

VMs need to be powered off if they are running CPU feature sets from a newer processor generation than what you are trying to set in EVC. E.g. If the VM is running (and was powered on) on a Haswell generation processor but you are trying to set the EVC to Sandy Bridge.

What generation CPUs do you have in your cluster and what EVC mode are you trying to set to?

If the validation is successful then you can enable it without any issue. However, if you reboot any VM before setting the EVC, the rebooted VM will start using the full feature set of the physical CPU and if you are setting the EVC to a older generation than the physical CPU, then you will need to power off that VM. Same applies if a VM has migrated between same generation CPU.

[samcatoe]

I am trying to set it to Nehalem.

I know one devices has rebooted on the "older" CPU, but I don't believe any device has rebooted on the newer CPU.

So as long as I haven't rebooted any machines since moving it from an EVC Compatible cluster, I can enable EVC Compatibility on the cluster with no issues?

[dineshgoundar]

Yes as long as no VM has rebooted/powered on on a newer generation host, you will be able to enable EVC. Its always a good idea to have EVC enabled even though you have hosts with the same generation processor.

[samcatoe]

Thanks so much for your help and assurance, I turned it on and was able to migrate the machines through the cluster.