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* The first recommended tool is again `fio` with `-ioengine=rbd -pool=<your pool> -rbdname=<your image>`. All of the above tests valid for raw drives can be repeated for RBD and they mean the same things, just sync. Sync, direct and invalidate flags don't mattercan be omitted, because RBD has no concept of "sync" - «sync» — all operations are always "sync"«sync». And there's there’s no page cache involved either, so "direct" «direct» also doesn't doesn’t mean anything.* The second recommended tool, especially useful for hunting performance problems, comes in the several improved varieties of "Mark's bench" «Mark’s bench» from russian Ceph chat: https://github.com/rumanzo/ceph-gobench or https://github.com/vitalif/ceph-bench. Both use a non-replicated Ceph pool (size=1), create several 4MB objects (16 by default) in each separate OSD and do random single-thread 4kb writesin randomly selected objects within one OSD. This mimics random writes to RBD and allows to determine the problematic OSDs by benchmarking them separately.Original Mark’s bench (outdated) was here: https://github.com/socketpair/ceph-bench

* And you can also use it from inside your VMs, the results are usually similar to the above. Just note that the result also depends on the storage driver being used. Virtio is the fastest, virtio-scsi is slightly slower and everything else (like LSI emulation) is terribly slow. Results are also considerably affected by whether the RBD cache is enabled or not (RBD cache turns on automatically with cache=writeback/none). For random reads or writes, disabling RBD cache is faster.