[Fedora-xen] resizing Xen para-virtualized guest partition

[Daniel P. Berrange]

On Mon, May 07, 2007 at 08:41:29PM -0400, Paul Wouters wrote:
> On Tue, 8 May 2007, John Summerfield wrote:
> 
> > btw You can create sparse files in the first place:
> > dd if=/dev/zero of=/tmp/ext-fs seek=$((4*1024*1024)) count=0
> > mke2fs -F -q /tmp/ext-fs
> 
> I understood that using sparse files will significantly slow down
> the xenu for the first time, as it keeps growing the fs allocation
> underneath it.

That is correct. Never use sparse files if you care about performance
as they exhibit pathelogically bad behaviour while growing the allocation.
Pre-allocation a file should give the best performance for file backed
guests, as close as you'll get to native without using physical devices
directly.

With a little tweaking to the dd command shown above though it ought to
be possible to extend the image, while allocating the data. You basically
want to seek=<current end of file>  and then count=<additional space>
desired.

Dan.
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