[sheepdog-users] Concern about sheepdog performance

[Valerio Pachera]

0.5.5_6_gb3f888b

journal is on a separated device (sdb) on all three nodes.

WITHOUT CACHE AND JOURNAL
- /mnt/sheepdog and /mnt/sdb1/sdj are using xfs with
'noatime,barrier=0' mount options.
- sheep -j dir=/mnt/sdb1/sdj,size=512 -w object:size=20000 /mnt/sheepdog/
- kvm -drive file=sheepdog:test
- on the guest: dd if=/dev/zero of=/mnt/sda1 bs=1M count=512
  8.9M/s

WITH CACHE AND JOURNAL
- -drive file=sheepdog:test,if=virtio,cache=writeback
- on the guest: dd if=/dev/zero of=/mnt/vda1 bs=1M count=512
  190M/s

WITH CACHE AND JOURNAL WRITING FILE TWICE
- on the guest: dd if=/dev/zero of=/mnt/vda1 bs=1M count=512
  242M/s

TIME USED BY SYNC
Correct me if I'm wrong:
  dd report a 'fake' speed because the is not yet written on disks,
but it's on cache.

To know fast data is synced from cache to disks I used this:
  sync; time (dd if=/dev/zero of=/mnt/vda1 bs=1M count=512; sync)
This way I know the elapsed time between dd starts and sync is done
writing data.

WITH CACHE AND JOURNAL
  26.8 s -> 512/26.8 = 19,1M/s

I tried also to remove 'noatime,barrier=0' mount options, and it seems
there's no difference.


WITH CACHE AND JOURNAL WRITING FILE TWICE
  25,3 s -> 512/25.3 = 20,2M/s