Virtual Machine and Host High Availability - Getting Started with Red Hat Enterprise Virtualization - page 106

Automatic virtual machine migration
Red Hat Enterprise Virtualization will automatically initiate the live migration of all the
running virtual machines that are marked as highly available and not pinned on a specific
host when the host is moved to the maintenance mode. This will be specifically helpful in a
scenario such as the major hardware fault of the hosts running hundreds of virtual machines
during critical business hours so that the admin does not need to manually select all the
hundred virtual machines and migrate them manually.
During the course of automatic virtual machine migration, the destination host in which
these virtual machines are to be placed will be selected based on the cluster policy defined
for the cluster. By default, the cluster policy is selected as none and it's strongly recommen-
ded that you select the cluster policy of either load balancing or power saving, whichever
suits your environment.
When a virtual server is automatically migrated because of the high-availability function,
the details of the automatic migration are documented in the Events tab of the RHEV Man-
ager console.
Note
In the case of hardware failure of one of the hypervisors in a cluster that runs two hypervi-
sor hosts, only virtual machines marked as highly available will be restarted, provided that
there are enough compute resources available on the second host. The rest of the virtual
machines will be in the power-down state even though they're marked highly available due
to resource constraints.