VMware 4817V62 - vSphere - PC Administration Manual page 191

Change the EVC Mode for an Existing Cluster
If all the hosts in a cluster are compatible with the new mode, you can change the EVC mode of an existing
EVC cluster. You can raise the EVC mode to expose more CPU features, or lower the EVC mode to hide CPU
features and increase compatibility.
To raise the EVC mode from a CPU baseline with fewer features to one with more features, you do not need
to turn off any running virtual machines in the cluster. Virtual machines that are running do not have access
to the new features available in the new EVC mode until they are powered off and powered back on. A full
power cycling is required. Rebooting the guest operating system or suspending and resuming the virtual
machine is not sufficient.
To lower the EVC mode from a CPU baseline with more features to one with fewer features, you must first
power off the virtual machines in the cluster, and power them back on after the new mode has been enabled.
Prerequisites
If you intend to lower the EVC mode, power off the currently running virtual machines in the cluster.
Procedure
1 Display the cluster in the inventory.
2 Right-click the cluster and select Edit Settings.
3 In the left panel, select VMware EVC.
The dialog box displays the current EVC settings.
4 To edit the EVC settings, click Change.
5 From the VMware EVC Mode drop-down menu, select the baseline CPU feature set you want to enable
for the cluster.
If the selected EVC Mode cannot be selected, the Compatibility pane displays the reason or reasons why,
along with the relevant hosts for each reason.
6 Click OK to close the EVC Mode dialog box, and click OK to close the cluster settings dialog box.
CPU Compatibility Masks
CPU compatibility masks allow per-virtual machine customization of the CPU features visible to a virtual
machine.
vCenter Server compares the CPU features available to a virtual machine with the CPU features of the
destination host to determine whether to allow or disallow migrations with VMotion.
Default values for the CPU compatibility masks are set by VMware to guarantee the stability of virtual
machines after a migration with VMotion.
In some cases, where a choice between CPU compatibility or guest operating system features (such as NX/XD)
exists, VMware provides check-box options to configure individual virtual machines through the virtual
machine's Advanced Settings option. For more control over the visibility of CPU features, you can edit the
virtual machine's CPU compatibility mask at the bit level.
C Manual edit of the CPU compatibility masks without the appropriate documentation and testing
AUTION
might lead to an unsupported configuration.
VMware, Inc.
Chapter 16 Migrating Virtual Machines
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