[Qemu-devel] Re: [RFC][STABLE 0.13] Revert "qcow2: Use bdrv_(p)write_sync for metadata writes"

[Anthony Liguori]

On 08/25/2010 08:07 AM, Avi Kivity wrote:
> > >   The next allocation can then be filled from memory, so the 
> > > allocation sync is amortized over many blocks.  A power fail will 
> > > leak the preallocated blocks, losing some megabytes of address 
> > > space, but not real disk space.
> >
> > It's a clever idea, but it would lose real disk space which is 
> > probably not a huge issue.
>
> Not real disk space since no pwrite() would ever touch the disk.  If 
> the image were copied, _then_ we'd lose the disk space, if the copy 
> command and filesystem don't optimize zeros away. \

Ok.

Regards,

Anthony Liguori

> > > > And that's it.  There is no scenario where the disk is corrupted.
> > >
> > > _if_ that's the only failure mode.
> >
> > If we had another disk format that only supported growth and metadata 
> > for a backing file, can you think of another failure scenario?
>
> I can't think of one, but that's not saying much.