[OpenAFS] no quorum elected
Tue, 03 Jun 2008 13:46:41 -0400
>> This, of course, is wrong in the case of AFS DB-Servers. The master-
>> server (usually the one with the lowest IP) has an additional half-
>> vote. So no split-brain possible here.
>When did we change this? All of the documentation I ever read said you
>needed three so you could have a quorum during such an outage...
It's one of those "it all depends on what you mean" kind of things.
With two database servers, if you lose the slave server, you will still
maintain quorum. But if you lose the master server, you will NOT be able
to elect quorum.
So if you want to tolerate the loss of any single database server, you
need a minimum of three. But it doesn't matter if there are an even or
odd number if the number is greater than three; as already mentioned,
the master gets an extra half vote (I was under the impression the
extra half vote was really put in place to handle the two server case,
but it also serves to make things if you have an even number of servers
and half of them are unavailable). As a side effect of the voting
algorithm, at least half of your database servers will never be elected
AFAICT, this is the way it's always been.