@bvitnik Thank you -- very useful information!

We have a small, two-host pool, having just added a new host. The master is a Dell R640 (Intel(R) Xeon(R) Gold 6150 CPU @ 2.70GHzIntel(R) Xeon(R) Gold 6150 CPU @ 2.70GHz) and the second, an R630 (Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz). I attempted to migrate a VM to the second host as a test and received the error:

"code": "VM_INCOMPATIBLE_WITH_THIS_HOST",
  "params": [
    "OpaqueRef:<UUID1>",
    "OpaqueRef:<UUID2>",
    "VM last booted on a CPU with features this host's CPU does not have."
  ],...

I don't see much other detail that seems to offer clues. How do I determine what the incompatibility actually is? If the incompatibility is determined, is there some means of disabling features to ensure capatibility?

I did try a different VM and the migration worked!?