Re: [Qemu-devel] image size - OS reports 720mb, but image file is 2.3 gig

[Joe Bogner <joebogner@gmail.com>]

WipeDisk did the trick on Windows. My physical disk image is now the
same size as what the guest OS reports.

WipeDisk - http://www.birdcomputer.ca/Software/SoftwareToC.html

Thanks for your help.


On Fri, 11 Feb 2005 15:03:04 +0000, Paul Brook <paul@codesourcery.com> wrote:
> On Friday 11 February 2005 14:18, Joe Bogner wrote:
> > Hello,
> >
> > I'm trying to create an win2k image that is as small as possible. I'd
> > like to be able to copy the image back and forth between machines so
> > that I have a complete win2k development image.
> >
> > According to win2k, the size is about 720mb. Originally win2k was
> > reporting the size to be about 1.2gig, but I was able to reduce it
> > through NTFS compression.
> >
> > Here's the dilemna. The physical image file is 2.3gig. I've run a
> > qemu-img convert -f qcow <input> -O qcow <output>, which took the
> > original 4.5 gig image down to 2.3 gig. With qemu-img compression, I
> > was able to get it down to 1.7gig.
> >
> > Why is there such a large discrepency between what win2k reports and
> > the physical image file on disk? Is there anything else I can do to
> > reduce it, aside from compressing the physical image file?
> >
> > 1.7 gig is still quite a bit to be shuffling around between machines.
> 
> Even if files have been deleted/compressed the data will still be there on the
> disk. qemu can't tell the difference between "useful" data, and unused data
> that can be discarded. You need to make sure all the unused space on the
> image is actually zeroed.
> 
> One way to achieve this would be to shrink the guest partition to its minimum
> size, then create a second partition on the unused space and explicitly zero
> that out (using dd from knoppix if necessary).
> 
> Paul
>