I received a question today about HA admission control policies, and more specifically about the “failover host” admission control policy. The question was why VMs were restarted on a different host then selected with the “Failover Host” admission control policy. Shouldn’t this policy guarantee that a VM is restarted on the designated host?
The answer is fairly straight forward, and I thought I blogged about this already but I cannot find it so here it goes. Yes, in a normal condition HA will request the designated failover host to restart the failed VMs. However there are a couple of cases where HA will not restart a VM on the designated failover host(s):
- When the failover host is not compatible with the virtual machine (portgroup or datastore missing)
- When the failover host does not have sufficient resource available for the restart
- When the virtual machine restart fails HA retries on a different host
Keep that in mind when using this admission control policy, it is no hard guarantee that the designated failover host will restart all failed VMs.