6 node vSAN - no VM FTT required

[nadeemsarwar]

we are planning a 6 node cluster, 3 + 3 nodes in two different rooms. Also we don't require any FTT for VMs as it is all instant clone work load. If we lose one room i.e 3 nodes does vSAN continue to work ?

From the documentation 2n+1 is the formula, where n is the failure. So to tolerate 3 failed nodes don't we need 7 nodes. Does the fact that we don't need any FTT for the VMs make any difference ?

Thanks

[TheBobkin]

Hello @nadeemsarwar

"If we lose one room i.e 3 nodes does vSAN continue to work ?"
From the nodes in the room that is still functional, vsanDatastore will still be accessible and usable (e.g. can still deploy new VMs to it) but if your data is stored as FTT=0 then all data that was stored on the failed room/site will be inaccessible until this is restored/fixed, so those VMs that now have inaccessible objects will crash and won't be restarted by vSphere HA and have to be redeployed (or fix the problem that resulted in). So while you say you don't need FTT from the perspective of being able to redeploy VMs, ensure that you understand that you are talking downtime for the users when this occurs (but that also being deployed, a 3+3 design wouldn't really protect from 3 nodes failing anyway, that would need a 3+3+1 stretched-cluster topology).

"From the documentation 2n+1 is the formula, where n is the failure. So to tolerate 3 failed nodes don't we need 7 nodes."
Yes, if you wanted ALL data to remain accessible with 3 of 6 nodes failed then it would require a RAID1 FTT=3 policy which requires 7 nodes for component placement (and a lot of space for replicas).

"Does the fact that we don't need any FTT for the VMs make any difference ?"
It sure does, but I'm not sure whether you have clarified whether you need VMs to be accessible following an outage or are okay with just redeploying them (which is not instantaneous).