On Mon, Aug 12, 2019 at 10:03 PM yangjun@xxxxxxxxxxxxxxxxxxxx <yangjun@xxxxxxxxxxxxxxxxxxxx> wrote: > > Hi Jason, > > I was recently testing the RBD mirror feature(ceph12.2.8), my test environment is a single-node cluster, which including 10 3T hdd OSDs + 800G pcie ssd + bluestore, and the wal and db partition of the OSD is 30G. > The test result of a 100G image is as follows： > > disable journal enable journal decline percentage > iops： 1000 877 12.3% > bw： 402MB/s 129MB/s 67% > > > Why does the bandwidth decline so much after starting journal of the RBD image? I'm very appreciate if you could give me some suggestions for optimization. Thank you very much. The use of the journal requires first writing to the journal and, once committed, writing to the image (i.e. doubling the latency). Therefore, the expected worst-case performance should be around 2x slower [1]. There was a recent bug fix [2] in the master branch that will be backported to older releases which greatly increases small IO journal performance -- since it was nearly 10x slower due to the bug instead of the expected 2x [3]. > ________________________________ > yangjun@xxxxxxxxxxxxxxxxxxxx [1] https://www.slideshare.net/JasonDillaman/disaster-recovery-and-ceph-block-storage-introducing-multisite-mirroring/17 [2] https://tracker.ceph.com/issues/40072 [3] https://youtu.be/ZifNGprBUTA?t=1687 -- Jason _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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