Hi , I am not sure why PG numbers have not given that much importance in the ceph documents, I am seeing huge variation in performance number by changing PG numbers. Just an example
*without SSD* : 36 OSD HDD => PG count 2048 gives me random write (1024K bz) performance of 550 MBps *with SSD :* 6 SSD for journals + 24 OSD HDD => PG count 2048 gives me random write (1024K bz) performance 250 MBps if I change it to 6 SSD for journals + 24 OSD HDD => PG count 512 gives me random write (1024K bz) performance 700 MBps Variation of PG numbers make SSD looks bad in number. I am bit confused here with this behaviour. Thanks sumit On Mon, Feb 9, 2015 at 11:36 AM, Gregory Farnum <g...@gregs42.com> wrote: > On Sun, Feb 8, 2015 at 6:00 PM, Sumit Gaur <sumitkg...@gmail.com> wrote: > > Hi > > I have installed 6 node ceph cluster and doing a performance bench mark > for > > the same using Nova VMs. What I have observed that FIO random write > reports > > around 250 MBps for 1M block size and PGs 4096 and 650MBps for iM block > size > > and PG counts 2048 . Can some body let me know if I am missing any ceph > > Architecture point here ? As per my understanding PG numbers are mainly > > involved in calculating the hash and should not effect performance so > much. > > PGs are also serialization points within the codebase, so depending on > how you're testing you can run into contention if you have multiple > objects within a single PG that you're trying to write to at once. > This isn't normally a problem, but for a single benchmark run the > random collisions can become noticeable. > -Greg >
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