EVC is just an automatic masking CPU features to level of least advanced CPU in cluster. So if you enable EVC on cluster with only one CPU model nothing is to mask and all features remain enabled.
Non-EVC cluster just do not have automatic masking and if you have the same CPU in Non-EVC cluster nothing prevents you from VM migration.
VMware vExpert '2009
The reason I need to enable EVC is because I have a new host which has a different CPU revision to the current hosts in the cluster. The CPU's will be compatible after EVC is enabled. My question is after EVC has been enabled will VM's be able to migrate from a non-EVC cluster to an enabled EVC cluster without switching off?
CPU's are quad core Intel Zeon. X53xx and X54xx.
As long as you use a host from the original cluster to create the new EVC cluster you should be fine.
below the procedure I used (just in case, but you probably know that)
Put host in maintenance mode
remove host from original cluster
create new EVC enabled cluster
add host to it (check NX/XD and Intel_VT options in system BIOS. These options need to be enabled)
VMotion files from old to new cluster.
disarm old cluster
-Arnim van Lieshout
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So, I suppose EVC will set cluster to 53xx level.
As far as I understand migration from 53xx Xeon to cluster will be possible, even if there are some 54xx in cluster. The only requirement - EVC cluster must contain 53xx.
But you won't be able to migrate VM from 54xx standalone to cluster with 53xx.
VMware vExpert '2009
If all the requirements for EVC are enabled within the BIOS on all hosts then migrating VMs should not be a huge issue however when they are not enabled, then you have to shutdown VMs and boot them on an EVC enabled node.
I have yet to perform one where I did not have to temporarily shutdown VMs. Perhaps you should use VMware HA to do this but make sure the target is a host enabled with EVC.....
Edward L. Haletky
VMware Communities User Moderator, VMware vExpert 2009
Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education.
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I know it's a few weeks ago, but I thought I'd let you know I was able to turn on EVC with no downtime. Here is how I did it.
5 host cluster which once EVC was enabled will be a 6 host cluster. Intel Zeon 53xx and Intel Zeon 54xx was causing me problems and therefore needed EVC working.
1) Put one of the existing live hosts into maintenace mode and remove from cluster.
2) Create new EVC enabled cluster with new host and host just removed from live cluster.
3) Migrate enough VM's to new cluster so I can put another host into maintenance mode and remove from live cluster then add to new cluster. This was the stage I thought would fail due to CPU masking issues, but it work fine.
4) Repeat until all VM's and hosts are in new cluster.
5) Recreate resource pools and configure cluster. (HA/DRS)
I hope this helps others. Any questions please ask.