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• it must have its virtual disks on shared storage (any type of shared storage may be used; the iSCSI, NFS or Fibre
Channel LUN is only required for the storage heartbeat and can be used for virtual disk storage if you prefer,
but this is not necessary)
• it must not have a connection to a local DVD drive configured
• it should have its virtual network interfaces on pool-wide networks.
Citrix strongly recommends the use of a bonded primary management interface on the servers in the pool if HA
is enabled, and multipathed storage for the heartbeat SR.
If you create VLANs and bonded interfaces from the CLI, then they may not be plugged in and active despite
being created. In this situation, a VM can appear to be not agile, and cannot be protected by HA. If this occurs,
use the CLI pif-plug command to bring the VLAN and bond PIFs up so that the VM can become agile. You can
also determine precisely why a VM is not agile by using the xe diagnostic-vm-status CLI command to analyze its
placement constraints, and take remedial action if required.
Restart Priorities
Virtual machines can assigned a restart priority and a flag to indicates whether or not they should be protected
by HA. When HA is enabled, every effort is made to keep protected virtual machines live. If a restart priority is
specified, any protected VM that is halted will be started automatically. If a server fails then the running VMs
will be started on another server.
An explanation of the restart priorities is shown below:
HA Restart Priority Restart Explanation
0 attempt to start VMs with this priority first
1 attempt to start VMs with this priority, only after having attempted to restart
all VMs with priority 0
2 attempt to start VMs with this priority, only after having attempted to restart
all VMs with priority 1
3 attempt to start VMs with this priority, only after having attempted to restart
all VMs with priority 2
best-effort attempt to start VMs with this priority, only after having attempted to restart
all VMs with priority 3
HA Always Run Explanation
True VMs with this setting are included in the restart plan
False VMs with this setting are NOT included in the restart plan
Warning:
Citrix strongly advises that only StorageLink Service VMs should be given a restart priority
of 0. All other VMs (including those dependent on a StorageLink VM) should be assigned a
restart priority 1 or higher.
The "best-effort" HA restart priority must NOT be used in pools with StorageLink SRs.
The restart priorities determine the order in which XenServer attempts to start VMs when a failure occurs. In a
given configuration where a number of server failures greater than zero can be tolerated (as indicated in the HA
panel in the GUI, or by the ha-plan-exists-for field on the pool object on the CLI), the VMs that have
restart priorities 0 1, 2 or 3 are guaranteed to be restarted given the stated number of server failures. VMs with a