Re: [Qemu-devel] qmp drive-mirror vs qemu-img convert , drive-mirror really slow

[Paolo Bonzini]

Il 21/01/2013 10:40, Alexandre DERUMIER ha scritto:
> Hi list,
> 
> I'm doing some speed benchmark between
> 
> drive-mirror vs qemu-img convert ,
> 
> and drive-mirror seem to be a lot slower.
> 
> 
> test:
> 
> convert 1 32GB qcow2 file to raw file, local storage (6 disk 15k in raid10 + 
> raid BBU cache)
> 
> time result:
> 
> qemu-img : 30sec
> drive-mirror (vm is paused, no writes) : 5min
> 
> 
> Any idea why drive-mirror is so slow ? (maybe does it use directsync when 
> mirroring ?)

No, it doesn't.  Probably it's because the image is sparse?  The current
code in git master has a very coarse granularity (1 MB).

Please try the blkmirror-job-1.4 branch from my github repo
(git://github.com/bonzini/qemu.git).  That branch uses the qcow2 file's
cluster size as the granularity, and has other optimizations that kick
in when the image is sparse.

Paolo

> I think both should have around same speed ?
> 
> 
> Best Regards,
> 
> Derumier Alexandre
> 
> 
>