[ceph-users] is unknown pg going to be active after osds are fixed?

Hi, With 3 replicas, a pg hs 3 osds. If all those 3 osds are down, the pg becomes unknow. Is that right? If those 3 osds are replaced and in and on, is that pg going to be eventually back to active? Or anything else has to be done to fix it? Thanks! Tony