Add vSAN Witness Node to Existing 3-Node Cluster

[OsburnM]

Greetings.  I have an existing 3-node vsan cluster that I want to upgrade; however, with RAID1/FTT=1, I am unable to do a full evac of the hosts to put them in maint-mode and do the upgrade.  I know I could just extend the object repair time and not do the full evac; however, it is critical data I don't want to risk not being able to rebuild if the cluster goes belly up.

I was thinking of adding a 4th host to the cluster temporarily as a vsan witness node only.  This would give my witness components some place to go while the host evacs.

Thoughts on this approach?  Can you deploy the pre-built witness node in this manner or do I need to deploy a full esx host & use the advanced flag to mark it a witness only host?

Thanks in advance!

[kastlr]

Hi,

a vSAN witness doesn't solve your problem, as it wouldn't store any vSAN objects except the witness objects.

What’s a vSAN Witness host?

If you need to run the upgrade AND it's required to perform a full data migration you would need an extra vSAN host.

Keep in mind that your whole data is migrated multiple times so depending on the amount of data you could expect that the upgrade would last a while.

[OsburnM]

Thanks for the reply though I guess I'm not following why a Witness-only node in this scenario wouldn't work?

I have 3 nodes today and all objects are RAID1/FTT1.  So that's 2 Nodes for the RAID1 components, and 1 node for the Witness components.  My thought here is if I have a Witness-only host, all the Witness components would go there, freeing up 1 "regular" esxi node's ability to evacuate?

[kastlr]

Got your point, it might work.

But you would need enough free disk space on each of those 3 physical vSAN Nodes.

And if your data is that critical that you require full RAID 1 redundancy during the upgrade it might not be the best approach to use a procedure which extremely differ from any standard.

Just my 2 cents.

[depping]

it won't work, vSAN Witness is intended for 2-node configurations and for stretched clusters... this is neither.

[amohammadimir]

I suggest you to read this:

https://core.vmware.com/resource/vmware-vsan-design-guide