[ceph-users] Re: Theory about min_size and its implications

but what is the problem with only one active PG? someone pointed out "split brain" but I am unsure about this.

I think Paxos will ensure that split-brain doesn’t happen by virtue of needing >50% of the mon quorum to be up.

i think what happens in the worst case is this: only 1 PG is available, client writes changes to this PG, the disk of this 1 PG dies as well

That’s part of it. Overlapping failures *do* happen.

- so i guess we'd need to restore the data from the 2 offline PGs in the room that is down and we would have lots of trouble with restoring and also with data inconsistency, right?

Yes.