Assuming ESXi 5.1 u2, If you have two clusters, one set at EVC = Westmere and one set at Haswell, could you vmotion a powered on vm from the lower level (Westmere) cluster to the higher level (Haswell) cluster or does it need to be powered off? I realize that to take advantage of the newer processor feature set, a power cycle of the vm is required, but I'm not clear if you can vmotion it while powered on?
Yes, you can vMotion a VM to a newer CPU generation host just fine provided it contains identical CPU instruction sets the older CPU has (and the host has them enabled in the BIOS too). You can also vMotion them back to the older hosts because as long as you haven't power-cycled the VMs, they will keep running with the old EVC baseline.
I also vMotioned VMs from Nehalem generation hosts to newer Sandy Bridge hosts a while back without issues.
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