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Re: [Xen-users] RHEL5 as PVM on RHEL5 xen

On Wed, Apr 11, 2007 at 01:00:06PM +0530, trilok nuwal wrote:
> On 3/30/07, Nico Kadel-Garcia <nkadel@xxxxxxxxx> wrote:
> >
> >trilok nuwal wrote:
> >> Ya,  this is a file disk made by "dd" and then formatted ext3 file
> >> system. Thats why i  able to mount this as i mention in earlier mail.
> >By the way, there are a lot of instructions about doing this out there
> >in the wild that insist on using "dd if=/dev/zero count=[some big
> >number]" to fill the entire disk image. Don't do that unless you want to
> >waste aa lot of time!

Well that really all depends on where you want to waste time.

If you create a sparse file, it is nice and fast for you to create initially.
The disk I/O performance of your guest will be absolutely *TERRIBLE* as it
causes the host to gradually allocate blocks behind the sparse file. So you
easily come out at a net loss.

If you create a non-sparse, fully allocated file, it takes a little while up
front, but the disk I/O performance of your guest will be excellant from the
moment it starts.

For dev / testing where you're never likely to actually use the whole of
the disk image, its worth doing sparse files, but for production where
performance of the guest matters, use non-sparse.

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