On Mon, Aug 13, 2018 at 10:44 AM Emmanuel Lacour <elac...@easter-eggs.com> wrote:
> Le 13/08/2018 à 16:29, Jason Dillaman a écrit : > > > > 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? > > > I looked at iostat on both cluster when running fio and yes, on new > cluster I see disks reads, but not with old cluster, everything comes from > page cache. > > So is there a way to simulate page cache for bluestore, or on rbd side? > See [1] for ways to tweak the bluestore cache sizes. I believe that by default, bluestore will not cache any data but instead will only attempt to cache its key/value store and metadata. In general, however, I would think that attempting to have bluestore cache data is just an attempt to optimize to the test instead of actual workloads. Personally, I think it would be more worthwhile to just run 'fio --ioengine=rbd' directly against a pre-initialized image after you have dropped the cache on the OSD nodes. [1] http://docs.ceph.com/docs/mimic/rados/configuration/bluestore-config-ref/ -- Jason
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