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4. Run the pool-ha-compute-max-host-failures-to-tolerate command. This command returns the
maximum number of hosts that can fail before there are insufficient resources to run all the protected
VMs in the pool.
xe pool-ha-compute-max-host-failures-to-tolerate
The number of failures to tolerate determines when an alert is sent: the system will recompute a failover
plan as the state of the pool changes and with this computation the system identifies the capacity of
the pool and how many more failures are possible without loss of the liveness guarantee for protected
VMs. A system alert is generated when this computed value falls below the specified value for ha-
host-failures-to-tolerate.
5. Specify the number of failures to tolerate parameter. This should be less than or equal to the computed
value:
xe pool-param-set ha-host-failures-to-tolerate=<2>
Removing HA protection from a VM using the CLI
To disable HA features for a VM, use the xe vm-param-set command to set the ha-always-run parameter
to false. This does not clear the VM restart priority settings. You can enable HA for a VM again by setting
the ha-always-run parameter to true.
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.