vCenter Server performs compatibility checks before it allows migration of running or suspended virtual machines to ensure that the virtual machine is compatible with the target host.
vMotion transfers the running state of a virtual machine between underlying ESXi systems. Live migration requires that the processors of the target host provide the same instructions to the virtual machine after migration that the processors of the source host provided before migration. Clock speed, cache size, and number of cores can differ between source and target processors. However, the processors must come from the same vendor class (AMD or Intel) to be vMotion compatible.
Do not add virtual ESXi hosts to an EVC cluster. ESXi virtual machines are not supported in EVC clusters.
Migrations of suspended virtual machines also require that the virtual machine be able to resume execution on the target host using equivalent instructions.
When you initiate a migration with vMotion or a migration of a suspended virtual machine, the Migrate Virtual Machine wizard checks the destination host for compatibility and produces an error message if compatibility problems will prevent migration.
The CPU instruction set available to the operating system and to applications running in a virtual machine is determined at the time that a virtual machine is powered on. This CPU feature set is based on the following items:
Host CPU family and model
Settings in the BIOS that might disable CPU features
ESX/ESXi version running on the host
The virtual machine's compatibility setting
The virtual machine's guest operating system
To improve CPU compatibility between hosts of varying CPU feature sets, some host CPU features can be hidden from the virtual machine by placing the host in an Enhanced vMotion Compatibility (EVC) cluster.
You can hide Host CPU features from a virtual machine by applying a custom CPU compatibility mask to the virtual machine, but this is not recommended. VMware, in partnership with CPU and hardware vendors, is working to maintain vMotion compatibility across the widest range of processors. For additional information, search the VMware Knowledge Base for the vMotion and CPU Compatibility FAQ.