Use EVC or not building new clusters?

[trink408]

Hello all,

curious what the community recommends in regards to using EVC on clusters or not? 

I'm building some new clusters, all the same hardware on the new hosts going into those clusters. I don't foresee adding any new hosts down the road into the cluster, but that could happen if demand got high enough that we needed more resources. 

I will migrate my existing VM's over to the new clusters, then retire my existing hosts. I'm thinking I will have to power off my vm's when migrating to the new cluster since the existing cluster is much older hardware.

Any thoughts or advice is appreciated.

Thank you,

[daphnissov]

Always enable EVC on net-new cluster builds. There's no reason not to and you future proof your migrations.

[Alex_Romeo]

Hi,

there are no reasons why you don't have to enable it, on the contrary it is advantageous.

https://www.vembu.com/blog/vmware-evc-mode-overview/

Benefits and Use Cases

Some might say, “why do I need this when I would certainly make sure the CPUs are identical when I configure my vSphere cluster ESXi hosts?”. In most greenfield deployments, this is most generally the case when the bill of materials is put together for the vSphere cluster hosts. Identical CPUs are chosen for the cluster hosts.

However, what happens two years later if you run out of compute capacity in your vSphere cluster and you need to scale out? You may not be able to build an exactly identical server build as you were when the cluster was originally configured. This means that most likely, any new servers will have slightly different hardware configurations, including the CPU configured.

The VMware EVC mode for the cluster would allow you in that case to set the specific CPU model type and instruction set that will be presented at the cluster level. New hosts that are added to the vSphere cluster would inherit those EVC settings and present only the specified CPU instruction set and features. This allows you to effectively scale out some time in the future without the worry of having different CPU configurations.

ARomeo

[trink408]

Thank you.

Do you recommend just setting EVC to the highest level when building a new cluster?

[daphnissov · Accepted solution]

Yes, unless you know or expect you'll have less capable servers possibly entering that cluster, the general recommendation is to select the highest EVC level which is compatible across all hosts.

[trink408]

One more question, how do I verify what the latest version of the EVC mode is? 

Thank you,

[daphnissov]

When you go to enable EVC through vCenter, pick the top most selection from the pick list. It'll tell you if that's compatible with all your hosts.

[trink408]

I'm guessing that skylake is the most recent? 

[daphnissov]

Yes