VMware 4817V62 - vSphere - PC Administration Manual page 186

vSphere Basic System Administration
Use of Jumbo Frames is recommended for best VMotion performance.
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CPU Compatibility and Migration
vCenter Server performs a number of compatibility checks before allowing migration of running or suspended
virtual machines to ensure that the virtual machine is compatible with the target hosts.
VMotion transfers the running state of a virtual machine between underlying ESX/ESXi systems. Successful
migration requires that the processors of the target host be able to execute using the equivalent instructions
that the processors of the source host were using when the virtual machine was migrated off of the source host.
Processor clock speeds and cache sizes, and the number of processor cores can vary, but processors must come
from the same vendor class (AMD or Intel) and use compatible feature sets to be compatible for migration with
VMotion.
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 there are
compatibility problems that will prevent migration.
When a virtual machine is powered on, it determines its available CPU feature set. The virtual machine's CPU
feature set is based on the host's CPU feature set. However, some of the host CPU features can be hidden from
the virtual machine if the host is part of a cluster using Enhanced VMotion Compatibility (EVC), or if a CPU
compatibility mask is applied to the virtual machine.
N VMware, in partnership with CPU and hardware vendors, is working to maintain VMotion
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compatibility across the widest range of processors. For additional information, search the VMware
Knowledge Base for the VMotion and CPU Compatibility FAQ.
CPU Compatibility Scenarios
vCenter's CPU compatibility checks compare the features available on the source and target host CPUs. A
mismatch in user-level features blocks migration. A mismatch in kernel-level features does not block migration.
When you attempt to migrate a virtual machine with VMotion, one of the following scenarios applies:
The destination host feature set matches the virtual machine's CPU feature set. CPU compatibility
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requirements are met, and migration with VMotion proceeds.
The virtual machine's CPU feature set contains features not supported by the destination host. CPU
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compatibility requirements are not met, and migration with VMotion cannot proceed.
The destination host supports the virtual machine's feature set, plus additional user-level features (such
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as SSE4.1) not found in the virtual machine's feature set. CPU compatibility requirements are not met, and
migration with VMotion cannot proceed.
The destination host supports the virtual machine's feature set, plus additional kernel-level features (such
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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.
186 VMware, Inc.