will the VM/Host Rules conflict with vSAN?

[nblr06]

Wondering about how does the VM/Host Rule work with vSAN FTT policy...

If there's a VM/Host Rule forcing a VM(say A) to run only on a specific vSAN host(say B) in a vSAN cluster, in which the vSAN policy is FTT=1 applied on A.

(Assume that the cluster DRS and HA were enabled with default setting, and is in vSphere version 6.7+)

What would happen on A if B goes down completely(failure)? Can A still run on other host in this vSAN cluster?

If all the vSAN disk groups failed in B, will A still be able to run in B?

Not sure about whether this is relate to the "vSAN Host Affinity storage policy"

Does anyone know?

[dimyke · Accepted solution]

Hi

The only items that are working together are failure domains.
When you create a failure domain, vSAN will use these as - the word says it - failure domain and will built the policy using these failure domains.

So if you have an FTT=1 and 6 hosts in 3 FD's then vSAN will put a data block in 2 different FD's and a whitness in the other remaining FD.

If you have an affinity rule binding a VM to a host and this host goes down then it will not have impact or be impacted from vSAN whatsoever.
So the answer to your question is not related to vSAN and only related to affinity rules, HA and what you have configured the VM to do.
In your case if you would create an affinity rule to have the VM on one host only, the VM will go down if the host goes down.
If you reconfigure this affinity rule to have the VM on another host,  a group of hosts or just remove the affinity rule after the host went down, the VM can be restarted on another host.
Or in case of a group of hosts, the VM will be restarted on another host in the group.

But again, there is no hard link between vSAN and affinity rules... Only fault domains have impact on how vSAN distributes its blocks.

I hope I made it somehow clear.

Kr
Dimitri