EVC. To use or not

[Viewaskew]

Question, if all the servers are of the exact same spec in a ESXi 5.x cluster, say for example all are Ivybridge and exactly the same CPU / server model, is it advisable to turn on EVC and set to Ivybridge or in fact to not enable it at all as there is no benefit seeing as all the CPUs are the same?

Thanks for any clarification.

[rcporto]

If all host are exactly the same there is no reason to enable EVC. Enable EVC on a cluster is recommend if your host have CPU from different generations and you want use vMotion across all host... what EVC will do is mask some features from newer CPU to make them with identical features like the older CPUs.

Anyway, some people recommends you enable EVC even if you use same CPU, but plans add hosts with different CPUs in the future... this way you will save some downtime to enable EVC later.

I will recommend you take a look at the following links

VMware KB: Enhanced vMotion Compatibility (EVC) processor support

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

[Gabrie1]

I think it depends on how big your environment is, how flexible you want to be and how much your environment will grow. For my datacenters I have chosen to enable EVC and set all blades to the Westmere level regardless of their real possible CPU level. Our environment has around 150 blades and we're constantly growing. We have many small clusters because of Microsoft licensing issues and I need to be very flexible when moving VMs. I don't want my host CPU to be a limiting factor when moving VMs around. When buying new blades I don't have to worry getting the same CPU type since most suppliers can only deliver the exact same hardware for a couple of months, but certainly not longer then 1 year.

From a technical point of view, I have had a discussion on this with Frank Denneman and he explained that the performance loss because of enabling EVC is maybe like 2-3%. Also, many new CPU features are not used by VMs anyway. So, from a technical point of view I see no reason to not enable EVC.

Also read this: http://frankdenneman.nl/2010/12/14/enhanced-vmotion-compatibility/