Specifications

n
The virtual machine’s CPU feature set contains features not supported by the destination host. CPU
compatibility requirements are not met, and migration with vMotion cannot proceed.
NOTE EVC overcomes such incompatibility by providing a "baseline" feature set for all virtual machines
running in a cluster and that hides the differences among the clustered hosts' CPUs from the virtual
machines.
n
The destination host supports the virtual machine’s feature set, plus additional user-level features (such
as SSE4.1) not found in the virtual machine’s feature set. CPU compatibility requirements are not met, and
migration with vMotion cannot proceed.
NOTE This type of incompatibility is ignored for migrations among hosts in EVC clusters.
n
The destination host supports the virtual machine’s feature set, plus additional kernel-level features (such
as NX or XD) not found in the virtual machine’s feature set. CPU compatibility requirements are met, and
migration with vMotion proceeds. The virtual machine retains its CPU feature set as long as it remains
powered on, allowing it to migrate freely back to the original host. However, if the virtual machine is
rebooted, it acquires a new feature set from the new host, which might cause vMotion incompatibility if
you attempt to migrate the virtual machine back to the original host.
CPU Families and Feature Sets
Processors are grouped into families. Processors within a given family generally have similar feature sets.
Processor families are defined by the processor vendors. You can distinguish different processor versions
within the same family by comparing the processors’ model, stepping level, and extended features. In some
cases, processor vendors have introduced significant architectural changes within the same processor family,
such as the SSSE3 and SSE4.1 instructions, and NX/XD CPU security features.
By default, vCenter Server identifies mismatches on features accessible to applications as incompatible to
guarantee the stability of virtual machines after migrations with vMotion.
Server hardware’s CPU specifications will usually indicate whether or not the CPUs contain the features that
affect vMotion compatibility.
For more information on identifying Intel processors and their features, see Application Note 485: Intel
®
Processor
Identification and the CPUID Instruction, available from Intel. For more information on identifying AMD
processors and their features, see CPUID Specification, available from AMD.
About Enhanced vMotion Compatibility
You can use the Enhanced vMotion Compatibility (EVC) feature to help ensure vMotion compatibility for the
hosts in a cluster. EVC ensures that all hosts in a cluster present the same CPU feature set to virtual machines,
even if the actual CPUs on the hosts differ. Using EVC prevents migrations with vMotion from failing because
of incompatible CPUs.
Configure EVC from the cluster settings dialog box. When you configure EVC, you configure all host processors
in the cluster to present the feature set of a baseline processor. This baseline feature set is called the EVC mode.
EVC leverages AMD-V Extended Migration technology (for AMD hosts) and Intel FlexMigration technology
(for Intel hosts) to mask processor features so that hosts can present the feature set of an earlier generation of
processors. The EVC mode must be equivalent to, or a subset of, the feature set of the host with the smallest
feature set in the cluster.
EVC masks only those processor features that affect vMotion compatibility. Enabling EVC does not prevent a
virtual machine from taking advantage of faster processor speeds, increased numbers of CPU cores, or
hardware virtualization support that might be available on newer hosts.
vCenter Server and Host Management
118 VMware, Inc.