Take this with a grain of salt, but you could try passing "min_io_size=<limited to 16bits>,opt_io_size=<RBD image object size>" as part of QEMU's HD device parameters to see if the OS picks up the larger IO defaults and actually uses them:
$ qemu <...snip...> -device driver=scsi-hd,<...snip...>,min_io_size=32768,opt_io_size=4194304 On Tue, Oct 17, 2017 at 5:12 PM, Russell Glaue <rgl...@cait.org> wrote: > I am running ceph jewel on 5 nodes with SSD OSDs. > I have an LVM image on a local RAID of spinning disks. > I have an RBD image on in a pool of SSD disks. > Both disks are used to run an almost identical CentOS 7 system. > Both systems were installed with the same kickstart, though the disk > partitioning is different. > > I want to make writes on the the ceph image faster. For example, lots of > writes to MySQL (via MySQL replication) on a ceph SSD image are about 10x > slower than on a spindle RAID disk image. The MySQL server on ceph rbd image > has a hard time keeping up in replication. > > So I wanted to test writes on these two systems > I have a 10GB compressed (gzip) file on both servers. > I simply gunzip the file on both systems, while running iostat. > > The primary difference I see in the results is the average size of the > request to the disk. > CentOS7-lvm-raid-sata writes a lot faster to disk, and the size of the > request is about 40x, but the number of writes per second is about the same > This makes me want to conclude that the smaller size of the request for > CentOS7-ceph-rbd-ssd system is the cause of it being slow. > > > How can I make the size of the request larger for ceph rbd images, so I can > increase the write throughput? > Would this be related to having jumbo packets enabled in my ceph storage > network? > > > Here is a sample of the results: > > [CentOS7-lvm-raid-sata] > $ gunzip large10gFile.gz & > $ iostat -x vg_root-lv_var -d 5 -m -N > Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz > avgqu-sz await r_await w_await svctm %util > ... > vg_root-lv_var 0.00 0.00 30.60 452.20 13.60 222.15 1000.04 > 8.69 14.05 0.99 14.93 2.07 100.04 > vg_root-lv_var 0.00 0.00 88.20 182.00 39.20 89.43 974.95 > 4.65 9.82 0.99 14.10 3.70 100.00 > vg_root-lv_var 0.00 0.00 75.45 278.24 33.53 136.70 985.73 > 4.36 33.26 1.34 41.91 0.59 20.84 > vg_root-lv_var 0.00 0.00 111.60 181.80 49.60 89.34 969.84 > 2.60 8.87 0.81 13.81 0.13 3.90 > vg_root-lv_var 0.00 0.00 68.40 109.60 30.40 53.63 966.87 > 1.51 8.46 0.84 13.22 0.80 14.16 > ... > > [CentOS7-ceph-rbd-ssd] > $ gunzip large10gFile.gz & > $ iostat -x vg_root-lv_data -d 5 -m -N > Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz > avgqu-sz await r_await w_await svctm %util > ... > vg_root-lv_data 0.00 0.00 46.40 167.80 0.88 1.46 22.36 > 1.23 5.66 2.47 6.54 4.52 96.82 > vg_root-lv_data 0.00 0.00 16.60 55.20 0.36 0.14 14.44 > 0.99 13.91 9.12 15.36 13.71 98.46 > vg_root-lv_data 0.00 0.00 69.00 173.80 1.34 1.32 22.48 > 1.25 5.19 3.77 5.75 3.94 95.68 > vg_root-lv_data 0.00 0.00 74.40 293.40 1.37 1.47 15.83 > 1.22 3.31 2.06 3.63 2.54 93.26 > vg_root-lv_data 0.00 0.00 90.80 359.00 1.96 3.41 24.45 > 1.63 3.63 1.94 4.05 2.10 94.38 > ... > > [iostat key] > w/s == The number (after merges) of write requests completed per second for > the device. > wMB/s == The number of sectors (kilobytes, megabytes) written to the device > per second. > avgrq-sz == The average size (in kilobytes) of the requests that were issued > to the device. > avgqu-sz == The average queue length of the requests that were issued to the > device. > > > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- Jason _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
