Hello Max, Good Day !
We have been testing more combinations of fail-over and arbiter combinations of 1 and 3.
The main observation that stood out is, writeMajority is not affected by the number of arbiter nodes. i.e. if there are two data nodes, P and S, then the writeMajority is always 2, even if Arbiters are 1 or 3.
Only difference as you pointed out, majorityvotecount would be 2 for the replicaset if there is only 1 arbiter, while it would be 3 if there are a total of 5 nodes (including 3 arbiters).
Also the statement PSAAA won’t move forward is not true, as the number of data bearing nodes is unchanged from 2 irrespective of 1 arbiter or 3 arbiters.
Also the hypothetical situation you mentioned that all 3 arbiter nodes might be down, would still be possible even for the single arbiter as well. So there’s no difference.
Sorry for the persistence on this. But we need to vet this down to ensure there are no shortcomings in our testing.
Thanks again for your help.