Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format

[Anthony Liguori]

On 09/10/2010 06:25 AM, Avi Kivity wrote:
>  On 09/10/2010 02:14 PM, Avi Kivity wrote:
> > > qcow2 is not a properly designed image format.  It was a weekend 
> > > hacking session from Fabrice that he dropped in the code base and 
> > > never really finished doing what he originally intended.  The 
> > > improvements that have been made to it are almost at the heroic 
> > > level but we're only hurting our users by not moving on to something 
> > > better.
> >
> > I don't like qcow2 either.  But from a performance perspective, it 
> > can be made equivalent to qed with some effort.  It is worthwhile to 
> > expend that effort rather than push the burden to users. 
>
> btw, despite being not properly designed, qcow2 is able to support 
> TRIM.  qed isn't able to, except by leaking clusters on shutdown.  
> TRIM support is required unless you're okay with the image growing 
> until it is no longer sparse (the lack of TRIM support in guests make 
> sparse image formats somewhat of a joke, but nobody seems to notice).

It's actually pretty easy in QED and it should perform very well.

http://wiki.qemu.org/Features/QED/Trim

Regards,

Anthony Liguori