Working on procedure to follow when we have any power outage.
Last power outage, we tried shutting down all VMs, but some vhosts died before others when UPS battery ran out and HA started booting up those hosts on remaining vhosts, which is the last thing we wanted to have happen while trying to shut everything down.
My question is whether putting all vhosts into maintenance mode will prevent that from happening?
I know putting vhosts into maintenance mode only completes once the last running VM is migrated off it, but if, before that, another vhost dies, can HA still power up VMs on the host for which "Enter maintenance mode" has been initiated, but not completed?
No, if you already started the maintenance mode in the ESXi. VMs will not be moved there or powered on by HA.
Anyways, I think that in this scenario, what you can do is Disable "Host Monitoring for HA". So you will ensure that no VM will be powered on if you loose one host for the power issues
As soon as a host is asked to enter maintenance mode it is no longer a valid target for VMs within the cluster.