[et-mgmt-tools] Question about Guest disk image size limit

Daniel P. Berrange berrange at redhat.com
Mon Jul 2 18:28:20 UTC 2007

On Mon, Jul 02, 2007 at 07:25:09PM +0100, Richard W.M. Jones wrote:
> Jason Dunn wrote:
> >I found this post from a few months back, and was wondering if anyone 
> >knew when this fix would make its way into RHEL5 if ever?  In the mean 
> >time, does anyone know what I could change that would allow me to have 
> >larger than 16GB image files for guest OS's?
> The problem is literally just in the virt-manager UI (and it's been 
> fixed there since virt-manager 0.4.0).  So there are several things you 
> could do in the meantime, including upgrading to a recent virt-manager 
> using the FC6/F7 src RPM, or using /usr/sbin/virt-install directly, or 
> (I think this will work?) creating the disk image first by hand.

Actually, since you're very unlikely to need > 16 GB for the initial
install, by far the simplest option is to just extend the image once
you've completed the initial install. dd can do it trivially with

   dd if=/dev/zero of=/var/lib/xen/images/blah.img bs=1M count=0 seek=102400

Will extend the image to 100 GB for example. NB count=0 so it never actually
writes any data to your disk - it is merely seek'ing to the new desired
size, creating a sparse extension.

It is possible you may want to extend it non-sparse - this is a little
trickier. You have to make set 'seek' to match the current size, and
then count to specify the additional size.

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