On Mon, Aug 13, 2018 at 10:01 AM Emmanuel Lacour <elac...@easter-eggs.com> wrote:
> Le 13/08/2018 à 15:55, Jason Dillaman a écrit : > > > >> >> so problem seems located on "rbd" side ... >> > > That's a pretty big apples-to-oranges comparison (4KiB random IO to 4MiB > full-object IO). With your RBD workload, the OSDs will be seeking after > each 4KiB read but w/ your RADOS bench workload, it's reading a full 4MiB > object before seeking. > > > yes you're right, but if we compare cluster to cluser, on new cluster, > rados bench is faster (2 times) rbd fio is 7 times slower. > > that's why I suppose rbd is th problem here, but I really do not > understand how to fix it. I looked at 3 old hammer cluster and two new > luminous/buestore clusters and those results are constants. I do not think > ceph decided to put bluestore > as default luminous filestore if random reads are 7 time slower ;) > For such a small benchmark (2 GiB), I wouldn't be surprised if you are not just seeing the Filestore-backed OSDs hitting the page cache for the reads whereas the Bluestore-backed OSDs need to actually hit the disk. Are the two clusters similar in terms of the numbers of HDD-backed OSDs? > > (BTW: thanks for helping me Jason :) ). > > -- Jason
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