Re: [Qemu-devel] Re: [PATCH v2 6/7] qed: Read/write support

[Anthony Liguori]

On 10/13/2010 09:07 AM, Stefan Hajnoczi wrote:
> > > That means we can maintain the physical size without introducing
> > > additional fsync()s in the allocation path.  Since we're already
> > > writing out the header anyway, the write operation is basically
> > > free too.
> > >        
> > I don't see how it is free.  It's an extra write.  The good news is
> > that it's very easy to amortize.
> >      
> We only need to update the header field on disk when we're already
> updating the header, so it's not even an extra write operation.
>    

Because we're already writing out the sector that contains that field in 
the header.

Regards,

Anthony Liguori

> Stefan
>