Take the following system, a Supermicro VMware ESXi host with Intel Westmere E5645 CPUs.
Part of our deployment process is to set the appropriate Enhanced vMotion Capability (EVC) level for the vSphere cluster to avoid problems during possible future expansion. The Intel E5645 CPU is a mid-range Westmere CPU. However, VMware does not allow us to set EVC for this CPU model. It does work if we drop one level to the "Nehalem" mode.
What is the reason for this?
Intel AES-NI feature was disabled in the BIOS on the host servers. Enabling it allowed me to use the Westmere EVC level.