[sheepdog-users] Different write speed between vdi

[Liu Yuan]

On Mon, Aug 12, 2013 at 06:56:33PM +0800, Liu Yuan wrote:
> On Mon, Aug 12, 2013 at 09:54:59AM +0200, Valerio Pachera wrote:
> > After I've been taking the snapshot of vdi 'backup', write speed went
> > from 15 to 6/7 M/s and it doesn't change even if I rewrite multiple
> > times a file.
> > I also tried to remove the snapshot and rewrite the same file several
> > time and the speed is still 6/7 M/s (except once).
> > Am I misunderstanding 'only first write will be slowed down'?
> > 
> 
> No. It seems something goes wrong. I'll check it.

I can't reproduce the issue on my laptop. I tried 

-drive file=sheepdog:test,if=virtio -drive file=sheepdog:test2,if=virtio

to start VM, and dd these two vdis.

  Name        Id    Size    Used  Shared    Creation time   VDI id  Copies  Tag
s test         1  200 MB  200 MB  0.0 MB 2013-08-12 19:23   7c2b25     1           tag
  test         0  200 MB  0.0 MB  200 MB 2013-08-12 19:23   7c2b26     1              
  test2        0  200 MB  200 MB  0.0 MB 2013-08-12 19:23   fd3815     1        

You can see that test is a vdi with objects shared with 'snapshot test', test2
is a normal vdi. I got almost the same performance for test and test2 by

dd if=/dev/zero of=/dev/vdx bs=1M count=100 oflag=direct.

Thanks
Yuan