A common failure is some type of host failure that renders ESXi unable to keep running virtual machines. This could be a power failure, a host kernel crash or something else.
vSphere HA will take over and restart virtual machines on other hosts when a host failure has been detected.
In this environment, there is a VM named VM02 running on host ac-esxi-a-01:
A host failure occurs and is marked as lost:
At this point, vSphere HA kicks in and restarts the VM on another host. Since this environment as a rule that this VM should only be on hosts in host group A, it is restarted on an “A” host.
This behavior is not unique to vSphere HA and ActiveCluster—this is a property of shared storage in general when combined with vSphere HA. The true benefit of ActiveCluster with vSphere HA is when all of the compute goes down in the site local to a set of VMs.
Continuing with the failure above, the remaining 3 hosts in host group A fail too (the four of them comprise all hosts in datacenter A). Since there are no hosts left in host group A, vSphere HA follows the “should” rule and has not choice but to reboot them on hosts in host group B which are in the other datacenter.
Since ActiveCluster presents the same VMFS datastore to both datacenters from a FlashArray in each datacenter, the hosts in the remote datacenter can reboot the VMs from the failed hosts in a different datacenter with ease.
The behavior of host failure is not impacted by whether or not the cluster is configured for Uniform or Non-Uniform connectivity.