This morning, The Saffa Geek (@GreggRobertson5) sent out a tweet asking "Anyone know if one of my hosts in my ha cluster goes down will ha power on already powered off vm's from my down host?"
I decided to do some testing with HA and the different options for virtual machines with their end result.
Here is my vCenter environment. I have 2 hosts, 1 ESX and the other ESXi. You can see from this screenshot, the VMs that are powered off and powered on the ESXi host that will fail in my lab.
Here is a shot of the VM options for the Cluster Settings for HA (High Availability). I used the default for VM restart priority and Host Isolation Response was set to Power Off.
We will be testing a few things:
- A VM that is powered on with a restart priority using cluster settings (which is set to Medium; default) -- Scorpion-XPpro
- A VM that is powered off with a restart priority using cluster settings (which is set to Medium; default) -- Sektor-W28
- A VM that is powered on with a restart priority set to High -- Raiden-W2k8Ent
- A VM that is powered off with a restart priority set to High -- Reptile-W2k3EntR2
- A VM that is powered on with a restart priority set to Disabled -- VShield-DOITLIVE (removed DRS rules for vShield Zones)
- A VM that is powered off with a restart priority set to Disabled -- VShield-DMZtest (removed DRS rules for vShield Zones)
Let's start the HA simulation by powering off our virtual ESXi host. After 30 seconds we see the error show up
The host is down. But what are all the VMs doing?
It looks like our High Priority VM that was turned on is booting up
Our High Priority VM that was powered down, is still down but has now been registered on the new host.
Conclusion: vCenter HA (High Availability) sees all the VMs in their current state and will recreate that VM Power State on another VM if the restart priority is not disabled.
| VM Power State | Restart Priority | HA Action |
| On | High | The VM is registered on an existing host within the cluster and the VM performs a "restart". Since it has a high priority it will be restarted before any other VMs with a medium or low priority. It works as if you hit the reset button on a physical desktop. The VM restoration time depends on boot time, applications, etc. |
| Off | High | The VM is registered on another host in the Cluster. The VM is not powered on even though it has a high restart priority. |
| On | Default (Medium) | The VM is registered on an existing host within the cluster and the VM performs a "restart". The VM restoration time depends on boot time, applications, etc. |
| Off | Default (Medium) | The VM is registered on another host in the Cluster. The VM will not power on. |
| On | Disabled | The VM is not registered on another host in the Cluster. The VM shows powered on but in a disconnected state. Yet, the VM is never moved and network connectivity is lost. Therefor, the VM never has the ability to power on from another host. The only way to get a VM to power back on is to unregister the VM and re-register it on a new host in the cluster to break the lock held on the files. |
| Off | Disabled | The VM is not registered on another host in the Cluster. The VM is not powered on because it was already off. |
Suggested Reading for customizing your environment for HA
- Understanding High Availability Host Isolation Response with Network Attached Storage - KB Article: 1018325
- vSphere Availability Guide (read the HA section)
- Yellow-Bricks.com - HA Deepdive