HA - Datastore PDL/Host Isolation response

[andvm]

Hi,

Is there any reason why you would not set the action to "Power off and restart VMs" when there is an PDL?

On the other hand I understand that with APD the issue might be temporary so leaving it to Disabled.

With regards to Host Isolation and in a vSAN cluster, heartbeats go via the same vSAN vmkernel, does this mean that an isolated host has lost access to the vSAN datastore?

Thanks

[depping · Accepted solution]

Couple of things, not sure if you are "only" using vSAN and also have traditional storage but:

1. vSAN doesn't do anything with PDL/APD states today, this means that if you only have vSAN as storage there's no need to configure it in HA
2. If you do have traditional storage as well, then I would highly recommend configured both APD and PDL. I don't see a situation where not configuring PDL makes sense. But I would say the same for APD. I think it always makes sense to configure it as when you hit an APD then the VM can't write to disk, which could be very problematic. HA can restart the VM on a healthy host, which is the smart thing to do.
3. When it comes to vSAN and a host isolation, when a host isolation occurs the VMs on that host indeed lose access to the vSAN Datastore. Hence we ALWAYS recommend customers to configure the isolation response to "power off" as that will ensure the VMs are powered off and can be safely restarted elsewhere

I hope that helps. A lot of these things are discussed in my book by the way, which you can download for free here:

Clustering Deep Dive eBook

[andvm]

Yes it does thank you, good to know as since default is "Disabled" I was hesitant to change it apart for Host failure.

Have both vSAN and traditional storage so am summarizing the best practice/recommended HA settings below:

Host failure -              Restart VMs

Host Isolation -          Power off and restart VMs

Datastore with PDL - Power off and restart VMs

Datastore with ADP - Power off and restart VMs

Assume safe to change all these for existing live clusters also?

Thanks

[depping]

Sure you can enable this when the cluster is running and has VMs running. No problem.

[vGuy]

Quick note on the below one though:

Host Isolation -          Power off and restart VMs

On vSAN cluster, as Duncan mentioned, Host isolation would be Power Off and restart VMs.

However, if you have a cluster with traditional storage and your management network is separate from VM network then you might want to consider leaving the VMs powered on.