I have one cluster which is running AMD Opteron 6176 CPUs, and I've just added a host with an Opteron 6278, which is obviously a later generation than the 6176. With EVC disabled, I cannot VMotion VMs from to the new host. With EVC enabled at Opteron Generation 3, which is the earliest, indeed only, mode supported by the 6176, I receive the error with the 6278 that: "The host's CPU hardware does not support the cluster's current Enhanced vMotion Compatibility mode. The host CPU lacks features required by that mode."
I have read that the AMD Opteron Gen 3 (no 3DNow!) mode enables compatibility between the 6100 and 6200 series CPUs, but my 6176 CPUs are not compatible with that mode.
Is there anything I can do, apart from finding an older server on eBay?
I think I have found the only workable solution, which is to power off all the VMs in the cluster, change the compatibility mode to G3 - No 3D Now!, add the new host, and then power the VMs back on.