This means that the storage cluster knows that some objects (or newer
copies of existing objects) exist, but it hasn't found copies of them.
+One example of how this might come about for a PG whose data is on ceph-osds
+A and B:
+
+* A goes down
+* B handles some writes, alone
+* A comes up
+* A and B repeer, and the objects missing on A are queued for recovery.
+* Before the new objects are copied, B goes down.
+
+Now A knows that these object exist, but there is no live ceph-osd who
+has a copy. In this case, IO to those objects will block, and the
+cluster will hope that the failed node comes back soon; this is
+assumed to be preferable to returning an IO error to the user.
First, you can identify which objects are unfound with::