[sheepdog-users] cache performance test

[Valerio Pachera]

sheep -w size=20000 /mnt/sheep/meta/,/mnt/sheep/dsk02

/mnt/sheep/meta is a ssd disk. Cache it stored here. No objects are
stored on the same physical disk.
/mnt/sheep/dsk02 is a mechanical sata disk, 7200 rpm like all the
other hdd of the cluster.

This is my guest
  qemu-system-x86_64 -enable-kvm -smp 2 -m 512 -drive
file=sheepdog:squeeze,cache=writeback -drive
file=sheepdog:big,cache=writeback
and is running on the node with the ssd.

vdi named 'big' is formatted with ext4 and is where is write.

I compare the write speed of the guest using cache, with the write
speed of the host writing directly on the ssd.



dd if=/dev/zero of=n bs=1M count=512 oflag=direct

Guest: 55 MB/s
Host: 130 MB/s

dd if=/dev/zero of=n bs=1M count=512

Guest: 103 MB/s
Host: 302 MB/s

Honestly I expected not to see such big difference (with oflag=direct)
between the two using cache.

What do you think?