When VMs are used on new ESX servers the CPU mask maybe left over from the ESX server that they were previously used on. This can cause problems when VMotioning to new ESX servers that have slightly different CPU/s. To get around this issue, we need to reset the CPU mask as part of the process when moving any VMs over to a different host / cluster.
The following explains how to reset the CPU Identification Mask to avoid this issue:
1) Shutdown the problem VM
2) From the VMWare Infrastructure client, go to “Edit Settings” (From the summary tab) on the VM in question.
3) Select the “Options” tab
4) Select “CPUID Mask” under the “Advanced” section
5) Click the “Advanced” button
6) Click “Reset All to Default” button
7) Click “OK” on all forms to apply the change.
You should now *hopefully* be able to VMotion this Virtual Machine across seeing as though the CPUID Mask has been reset to defaults – I would imagine that this gets reconfigured depending on what CPU the VM finds when it starts up again.
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