2-node cluster with witness local to one node

[MBrownWFP]

I know this would not be a supported production configuration but is it possible to run a 2-node VSAN cluster with the witness appliance living on one of two hosts? If this does work from a functional perspective are there any special considerations around configuration? Appreciate any feedback that is provided.

[TheBobkin]

Hello MBrownWFP​,

It's unsupported due to the fact that if you lose the node that the Witness components and/or VM reside on, you lose access to 2/3 of the components of all Objects and thus lose quorum and thus these become inaccessible - e.g. this wouldn't provide FTT=1 which is the main purpose of a 1+1+1 or 2+1 cluster.

Don't even consider doing this, not because it is 'unsupported' but because of the fundamental reasons of why it is unsupported.

Bob

[MBrownWFP]

Thanks for the response. I should provide some background: this setup would only be a lab environment for testing and validating host firmware and ESXi patching processes when VSAN storage is enabled (we want to include VSAN disk format upgrades in our testing). This is relevant to us as we run VSAN for primary storage in our Prod datacenter cluster.

My question was more "can this be configured". I understand why this is inherently broken from a fault tolerance perspective. We are not concerned with FTT as this cluster will contain nothing but dummy data.

[TheBobkin · Accepted solution]

Thanks for clarifying - glad to hear you are a) interested in testing stuff and b) understand to not use this configuration on anything stable.

No, there isn't anything actually preventing from running and/or storing Witness VM on hosts in the cluster and vsanDatastore.

You will get various compatibility warnings regarding the vNICs on vMotion but it if adequate networking routes exist on the destination node it will remained clustered.

Bob

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[MBrownWFP]

Excellent. I appreciate the input Bob!