EVC mode changing from westmere to Sandy bridge

[tdubb123]

I have evc enabled for westmere on my cluster. IS there any issues with switching to sandy bridge while all vms are running? 

has anyone had to do this? We got a vm that is not liking the westmere instruction set

[a_p_]

If all the hosts in the cluster support Sandy Bridge, there shouldn't be any issues  with changing the EVC mode.
Changing the EVC mode will not affect powered on VMs, but will only take effect for VMs that are power cycled.

André

[tdubb123]

is there a way to check if current running vms will be affected when powercycled  if I changed the evc mode to sandy bridge?

[sjesse]

No, meaning they will power on, but depending on if you application would be affected differently by the change in cpu instructions is impossible for us to say. Between those two I don't think there would be anything and I'd just change it , but I don't know your apps.

[tdubb123]

I found this

https://blogs.vmware.com/vsphere/2019/06/enhanced-vmotion-compatibility-evc-explained.html

Is per VM evc something I can set? 

Say my cluster is on westmere, can i modify a vm vmx file to enable sandy bridge instructions?

[sjesse]

Look at 

https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.vm_admin.doc/GUID-A1C095EF-1B0F-4C1...

Especially 

Important:If the virtual machine is in an EVC cluster and the per-VM EVC mode exceeds the EVC mode for the cluster, the virtual machine fails to power on. The baseline CPU feature set for the virtual machine must not contain more CPU features than the baseline CPU feature set of the cluster.

EVC basically hides cpu instructions from the vm, if you have both on the cluster one applies first, then the vm. So you can't add features to the vm that that cluster doesn't show.

[tdubb123]

ok so from what i understand 

1. I can raise my evc mode to sandy bridge on the cluster while vms are running. 

2. each vm needs to be completd powered off and powered on to take advantage of sandy bridge instruction sets

3. if the VM does not power on due to the new instruction set, then I will need to do modify the vmx file to hide the sandy bridge instruction sets?

4. Do i need to upgrade to the latest VM hardware version before raising evc mode to sandy bridge

[tdubb123]

I checked all my hosts in the cluster are using proc Xeon 6132 and 6248 gold which belongs to skylake and cascade lake class

and my current evc is westmere and all vms are running fine on westmere. 

does this mean I can bump up to sandy bridge or even skylake without any issues? I dont intend to add hosts with older procs than skylake to this cluster

[a_p_]

1. Yes
2. Yes
3. It's unlikely that yo will experience issues. However, if required you may configure per-VM-EVC from the GUI.
4. No, you don't, but you may consider to upgrade to HW version 9, 11 or later unless already set (see. e.g. https://kb.vmware.com/s/article/52085)

André

[a_p_]

>>> does this mean I can bump up to sandy bridge or even skylake without any issues? I dont intend to add hosts with older procs than skylake to this cluster
You can go directly to the latest supported EVC mode. Although it's not likely that you will see issues, nobody can guarantee it.

André

[tdubb123]

Vmware is saying I need to shutdown All the VMs in the cluster inorder to raise the EVC. 

Is there another way?

[sjesse]

Evacuate one host, and put it in a new cluster in the correct evc mode, then vmotion vms over. Then repeat as you empty hosts our and move them to the new cluster.

[tdubb123]

I am reading this and looks like in 7.0, I can raise EVC without shutting down vms? Never tried this anyone has any issues?

https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.vcenterhost.doc/GUID-6698B0EE-8B52-...

[a_p_]

>>> Vmware is saying I need to shutdown All the VMs in the cluster in order to raise the EVC.
Just go to the EVC configuration settings, and select the new EVC mode. If no incompatibilities are detected, the changes can be saved, otherwise you'll see what prevents you from changing the EVC mode.

André

[pdirmann01]

"Evacuate one host, and put it in a new cluster in the correct evc mode, then vmotion vms over. Then repeat as you empty hosts our and move them to the new cluster."

I've definitely executed this method before and it has worked for me.