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Recovering an Unreachable Host
If for some reason a host cannot access the HA statefile, it is possible that a host may become unreachable.
To recover your XenServer installation it may be necessary to disable HA using the host-emergency-ha-disable
command:
xe host-emergency-ha-disable --force
If the host was the pool master, then it should start up as normal with HA disabled. Slaves should reconnect and
automatically disable HA. If the host was a Pool slave and cannot contact the master, then it may be necessary to
force the host to reboot as a pool master (xe pool-emergency-transition-to-master) or to tell it where the new
master is (xe pool-emergency-reset-master):
xe pool-emergency-transition-to-master uuid=<host_uuid>
xe pool-emergency-reset-master master-address=<new_master_hostname>
When all hosts have successfully restarted, re-enable HA:
xe pool-ha-enable heartbeat-sr-uuid=<sr_uuid>
Shutting Down a host When HA is Enabled
When HA is enabled special care needs to be taken when shutting down or rebooting a host to prevent the HA
mechanism from assuming that the host has failed. To shutdown a host cleanly in an HA-enabled environment,
first disable the host, then evacuate the host and finally shutdown the host using either XenCenter or the
CLI. To shutdown a host in an HA-enabled environment on the command line:
xe host-disable host=<host_name>
xe host-evacuate uuid=<host_uuid>
xe host-shutdown host=<host_name>
Shutting Down a VM When it is Protected by HA
When a VM is protected under a HA plan and set to restart automatically, it cannot be shut down while this
protection is active. To shut down a VM, first disable its HA protection and then execute the CLI command.
XenCenter offers you a dialog box to automate disabling the protection if you click on the Shutdown button of
a protected VM.
Note:
If you shut down a VM from within the guest, and the VM is protected, it is automatically
restarted under the HA failure conditions. This helps ensure that operator error (or an errant
program that mistakenly shuts down the VM) does not result in a protected VM being left
shut down accidentally. If you want to shut this VM down, disable its HA protection first.
Host Power On
Powering on Hosts Remotely
You can use the XenServer Host Power On feature to turn a server on and off remotely, either from XenCenter or
by using the CLI. When using Workload Balancing (WLB), you can configure Workload Balancing to turn hosts on
and off automatically as VMs are consolidated or brought back online.
To enable host power, the server must have one of the following power-control solutions:
• Wake On LAN enabled network card.
• Dell Remote Access Cards (DRAC). To use XenServer with DRAC, you must install the Dell supplemental pack
to get DRAC support. DRAC support requires installing RACADM command-line utility on the server with
the remote access controller and enable DRAC and its interface. RACADM is often included in the DRAC
management software. For more information, see Dell’s DRAC documentation.