I was discussing something with one of my former colleagues a couple of days ago. He asked me what the impact was of running VMware View in an environment without HA.
To be honest I am not a View SME, but I do know a thing or two about HA/vSphere in general. So the first thing that I mentioned was that it wasn’t a good idea. Although VDI in general is all about density not running HA in these environments could lead to serious issues when a host fails.
Now, just imagine you have 80 Desktop VMs per host running and roughly 8 hosts in a DRS only cluster on NFS based storage. One of those hosts is isolated from the network…. what happens?
- User connection is dropped
- VMDK Lock times out
- User tries to reconnect
- Broker powers on the VM on a new host
Now that sounds great doesn’t it? Well yeah in a way it does, but what happens when the host is not isolated anymore?
Indeed, the VMs were still running. So basically you have a split brain scenario. The only way in the past to avoid this was to make sure you had HA enabled and had set HA to power off the VM.
But with vSphere 4 Update 2 a new mechanism has been introduced. I wanted to stress this, as some people have already made assumption that it is part of AAM/HA. It actually isn’t… The question for powering off the VM to recover from the split brain scenario is generated by “hostd” and answered by “vpxa”. In other words, with or without HA enabled ESX(i) will recover the split brain
Again, I am most definitely not a Desktop/View guy so I am wondering how the View experts out there look against disabling HA on your View Compute Cluster. (Note that on the Management Layer this should be enabled.)