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* Do not use `rados bench`. It creates a small number of objects (1-2 for a thread) so all of them always reside in cache and improve the results far beyond they should be.
* You can also use the simple `fio -ioengine=libaio` with a kernel-mounted RBD. However, that requires to disable some features of that RBD, because kernel client still lacks their support. Note that regardless of the overhead of moving data in and out the kernel, the kernel client is actually faster.
* 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 (cache=writeback qemu option turns on RBD cache automatically). For random reads or writes, disabling disabled RBD cache is faster.
== Why is it so slow ==
