[Qemu-devel] virtio-scsi vs. virtio-blk

[Stefan Priebe]

Hello list,

i wanted to start using virtio-scsi instead of virtio-blk, cause it 
offers the possibility to use discard / trim support.

Kernel: 3.5.0 on host and guest
Qemu-kvm: 1.1.1 stable

But i'm not seeing the same or nearly the same speed:

virtio-scsi:
rand. 4k:
  write: io=677628KB, bw=67709KB/s, iops=16927, runt= 10008msec
  read : io=697648KB, bw=69646KB/s, iops=17411, runt= 10017msec
seq 4m:
  write: io=8192MB, bw=817683KB/s, iops=199, runt= 10259msec
  read : io=5672MB, bw=565378KB/s, iops=138, runt= 10273msec

virtio-blk:
rand. 4k:
  write: io=1750MB, bw=179169KB/s, iops=44792, runt= 10001msec
  read : io=1388MB, bw=142073KB/s, iops=35518, runt= 10006msec
seq 4m:
  write: io=9776MB, bw=984522KB/s, iops=240, runt= 10168msec
  read : io=2980MB, bw=288970KB/s, iops=70, runt= 10560msec

Any ideas?

Greets,
Stefan