Ceph » rbd

$ ./rbd create --size 1 a
rbd: create error: (17) File exists
2016-03-09 12:35:46.151908 7f34f97af640 -1 librbd: rbd image a already exists

$ ./rbd create --size 1 a
rbd: create error: (17) File exists2016-03-09 12:35:46.592681 7f66aa8f7640 -1
librbd: rbd image a already exists

$ ./rbd create --size 1 a
rbd: create error: 2016-03-09 12:45:17.850540 7f2864e71640 -1 librbd: rbd image a already exists
(17) File exists

This is because an lderr within librbd queues a log entry, which gets written out to cerr from the logging thread. We should probably switch to using derr instead of cerr in rbd CLI.

There are more instances of this in other ceph tools, so another possible solution is to make log entries that correspond to errors synchronous. I don't think it's a good idea though - it would still leave us with two independent sources of error messages and is more of a bandaid.