I have a question about "tell bench" command. When I run this, is it behaving more or less like a dd on the drive? It appears to be, but I wanted to confirm whether or not it is bypassing all the normal Ceph stack that would be writing metadata, calculating checksums, etc.
One bit of behavior I noticed a while back that I was not expecting is that this command does write to the journal. It made sense when I thought about it, but when I have an SSD journal in front of an OSD, I can't get the "tell bench" command to really show me accurate numbers of the raw speed of the OSD -- instead I get write speeds of the SSD. Just a small caveat there. The upside to that is when do you something like "tell \* bench", you are able to see if that SSD becomes a bottleneck by hosting multiple journals, so I'm not really complaining. But it does make a bit tough to see if perhaps one OSD is performing much differently than others. But really, I'm mainly curious if it skips any normal metadata/checksum overhead that may be there otherwise. Thanks, - Travis
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