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matrix999
Contributor
Contributor
‎08-01-2018 11:04 AM

Enabling EVC when enabling VMs from one vCenter to another

  1. We moved all hosts from one vcenetr server to another running 6.5. EVC is not enable on the new cluster. It was enabled on the old one so I guess this was the first issue. If EVC was set the same on the destination cluster we would not be in this position but let me explain

We have a combination of Gen 8, Gen 9 and Gen 10 hosts. We are actually adding the GEN 10 hosts to the cluster

QUESTIONS:

1. With EVC disabled in the cluster I plan to enable EVC ASAP and this will cause absolutely no impact to VMs is my understanding. The EVC modes are supported by all hosts, Sandy Bridge as Gen 8 is the lowest spec in cluster

2. EVC being disabled means we have an issue. VMs can vMotion to equal or higher spec only. However, once VMs are on a higher spec, they will NOT be able to vMotion to a lower spec. What is the best way to avoid a power cycle if every VM? Is the unavoidable?

3. Our VMs are vDS port group. I read a few ways to disconnect hosts etc but we followed best practice for vDS Port group and moved VMs to vStandard first so I will jnot simply disconnect hosts and re-add

4. What could have been better here? Had I enabled EVC in the new cluster that would have avoid the power cycles right? If we are introducing Gen 10s that are empty this would work.

I probably answered all my own questions here.

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1 Reply
a_p_
Leadership
Leadership
‎08-01-2018 11:30 AM

Enabling EVC will not affect powered on VMs. It ensures that a common set of CPU features will be presented to newly powered on VMs.

Regarding your questions:

  1. No impact to powered on VMs. Btw. depending on the CPU model Gen8 hosts may support Sandy or Ivy-Bridge mode
  2. As mentioned above, CPU features are presented to a VM at power on. If a VM has been powered on on a host with more features, you cannot live migrate it to a host with less features. Cold migration is to only save option in such a case. With the latest Micocode/BIOS you may need to power cycle the VM's anyway, for e.g. Spectre/Meltdown remediation. So maybe you can combine the EVC configuration with a BIOS/Firmware upgrade to save yourselve some downtime.
  3. Sound like a good plan.
  4. You can basically add any host that supports the CPU features in the EVC cluster. Host without powered on VMs shouldn't cause any issues, only hosts with VMs that see newer CPU features cannot be added.

André

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