Based on the XenCenter Help Contents, the following is a description of the Restart Priority of virtual machines (VMs) and how to configure using the XenCenter management console:
- Select the VM in the Resources pane and click the HA restart priority tab.
- Choose Restart to guarantee a VM will be restarted if sufficient resources are available within the pool. They will be restarted before VMs with a Restart if possible priority.
- Restart if possible are not considered when calculating a failure plan, but one attempt to restart them will be made if a server that is running them fails.
- Restart is attempted after all higher-priority VMs are restarted, and if the attempt to start them fails, then it will not be retried.
- In an HA-enabled pool, to conserve XenServer host resources, use Do not restart on VMs that don’t always have to be powered on.