Specifications

Best Practices for Virtualizing and Managing Exchange 2013

Virtual Machine Priority and Affinity

If you deploy virtual machines on a host cluster, you can use VMM to configure priority settings for

them. With these settings, the cluster starts or places high-priority virtual machines before medium-priority

or low-priority virtual machines. This ensures that the high-priority virtual machines, like those running

Exchange Server, are allocated memory and other resources first, for better performance. Also, after a

node failure, if the high-priority virtual machines do not have the necessary memory and other resources

to start, the lower priority virtual machines will be taken offline to free up the necessary resources for the

high-priority machines. Virtual machines that are preempted are later restarted in priority order.

You can also configure priority settings in a virtual machine template so that any virtual machines created

with that template will have the specified virtual machine priority.

VMM also provides the ability for an administrator to influence the placement of virtual machines on the

nodes of the host cluster. As an administrator, you can do this by defining Preferred Owners and

Possible Owners for the virtual machines—ensuring that certain virtual machines can only run on certain

hosts, or certain virtual machines will never run on a particular host (Figure 43).

Figure 43: System Center 2012 SP1 Virtual Machine Manager – Preferred and Possible Ownership

Availability Sets

When you place multiple virtual machines in an availability set, VMM attempts to keep those virtual

machines on separate hosts whenever possible (Figure 44). This helps to improve continuity of service.

Another way to configure this setting is to use Windows PowerShell commands for failover clustering. In

this context, the setting appears in the Get-ClusterGroup listing and is called AntiAffinityClassNames. Note

that you can also configure availability sets in a service template to specify how virtual machines created

with that template should be placed on hosts.