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

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

[Alexandre DERUMIER]

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 ?)

I think both should have around same speed ?


Best Regards,

Derumier Alexandre

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
> 
> 
> 

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

[Alexandre DERUMIER]

>>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. 

I'll try that, thanks Paolo, I'll keep you in touch.


----- Mail original -----

De: "Paolo Bonzini" <pbonzini@redhat.com>
À: "Alexandre DERUMIER" <aderumier@odiso.com>
Cc: "qemu-devel" <qemu-devel@nongnu.org>
Envoyé: Lundi 21 Janvier 2013 11:35:40
Objet: Re: qmp drive-mirror vs qemu-img convert , drive-mirror really slow 

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
>
>
>