Query about EVC mode

[timbo475]

Hi all,

Recently I had to migrate some VMs from an old cluster (VSphere 5) to a new cluster (VSphere 6), with the new cluster having much newer hardware. Whilst trying to migrate the warnings about incompatible hardware appeared and I put the new cluster into EVC mode for Westmere. All the VMs were successfully migrated and work fine. All the hosts on the new cluster are exactly the same hardware.

I'd like to either remove EVC or set it to a 'higher' level to enable the newer CPU features. If I try and change it to anything above Westmere I get the warning 'The host cannot be admitted to the cluster's current Enhanced vMotion Compatibility mode', which is expected but I'm wondering what the best move is. I think understand the purpose of EVC (it's primarily designed to enable hosts with different hardware to be in a cluster together) but unsure of a few specifics.

I think what I need to do is shutdown all VMs and then I should be able to change EVC mode (to a 'higher' mode or disable) without casunig any problems on the VMs. does that sound right? I just want to make sure changing the EVC mode won't adversely impact the VMs. Does the VM hardware version make any difference or is EVC essentially transparent to the VMs?

Cheers,

Tim

[Mattallford]

Hi Tim,

You should be able to raise the level of EVC within a cluster while the virtual machines are running, provided all of the hosts within the cluster support the new EVC mode. This is one of the ideas of EVC mode. For example, you could have the EVC mode set to Sandy Bridge and have hosts that are using Sandy Bridge processors, and then introduce Ivy Bridge hosts into the cluster. When all of the Sandy Bridge hosts have been replace by Ivy Bridge, you can upgrade the EVC mode from Sandy Bride to Ivy Bridge non-disruptively. Virtual machines won't pick up the new baseline until they are powered off and powered back on again (note: a reboot will not work).

Can you confirm the exact model of the CPU in your newer vSphere 6 hosts?

Are you getting any more information with the warning, such as Powered on / suspended VMs may be using the CPU features?

[timbo475]

Thanks for the reply. Actually it got me thinking a bit. Where I thought I was 'raising' the level, it looks like I was trying to lower it. I was getting the warning about 'powered on/suspended VMs using the CPU features.

If I select one of the choices below Westmere (Sandy/Ivy Bridge or Haswell) it looks like it will let me proceed. Bit of a rookie error but I haven't been dealing with processor architectures for a while. The CPUs are Xeon E5-2690 v3.

If I disable EVC, will that just open-up all the CPU awesomeness it possibly can?

[Mattallford · Accepted solution]

I was wondering if you were going the other way in that list, it can be a bit confusing at start and as you've found, newer generations are added to the bottom of the list.

Your CPUs are Haswell generation, so I'd set EVC to Haswell.

If I disable EVC, will that just open-up all the CPU awesomeness it possibly can?

Disabling EVC will mean the the hosts will present their full capability to the VMs when the VM is powered on.

My suggestion is usually to leave EVC enabled. It allows for the most flexibility with almost no drawbacks.

Some further reading:

http://www.derekseaman.com/2012/09/how-much-does-evc-mode-matter-and-which.html

Example Architectural Decision – Enhanced vMotion Compatiblity | CloudXC

Cheers, Matt.