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VMware Enhanced VMotion Compatibility

With VMware ESX 3.5.0 Update 2, the VMware guys slipped in a feature named Enhanced VMotion Compatibility that will really prove to make virtual machines portable between hardware generations, potentially making hardware upgrades seamless to your end users.

Enhanced VMotion Compatibility ( EVC for short ) is turned on at the cluster level, and it basically sets up a baseline ( lowest common denominator of CPU instructions ) for that cluster so that the entire cluster only has a certain instruction set available for use, and masks out any new instructions that might be added in a new processor family. You must stay within the same processor vendor ( ie, AMD or Intel ) and you must have the same processor features turned on in the BIOS ( such as AMD-V and NX for AMD and XD and VT for intel ). The functionality is brilliant, but here is the rub: all of the VMs in the cluster need to be powered off to turn on this functionality. Even if all of your hardware is exactly the same.

The workaround for this is the following: Create a new cluster, enable EVC on the new cluster and then one by one put your hosts into maintenance mode evacuating all of your VMs and put the host into the new cluster, then manually VMotioning all of your VMs from one cluster to another. Using this workaround you lose a few things though: Cluster performance history, migration history, HA and DRS settings will have to be manually copied over and then lastly and most annoyingly all of your affinity and anti-affinity rules will need to be rebuilt on the new cluster.

The lesson to be learned here is that if you're setting up a new cluster, make sure that you enable Enhanced VMotion Compatibility from the start. It's a minor amount of work at the beginning of a cluster that can save you a ton of time later on and there is really no drawback to enabling it.

Labels: VMware ESX 3.5.0 Update 2 EVC Enhanced VMotion Compatibility

Posted by Dominic Rivera at Saturday, August 09, 2008.