Re: [Xen-users] Slow Disk access on SLES 10 install

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Sun, Mar 04, 2007 at 05:57:30PM -0800, D Sims wrote:
> 
> Matthias:
> 
> You were 100% correct.  That was the piece of information that I did not
> know that I needed.  As soon as I changed the setting in the
> /etc/xen/scripts/block  script from
> 
> do_or_die losetup -y "$loopdev" "$file"
> 
> do_or_die losetup  "$loopdev" "$file"
> 
> this made all the difference in the world.  
> 
> However, this does beg another question. What is the best practice for
> setting up a virtual disk for a guest domain?
> 
> Is it better to live with the possibility of data corruption on a host crash
> and have normal disk access, or turn the flag on and be protected against
> corruption, but suffer terrible performance.  Or is there a better way? 

Don't use 'file:'  at all - loopback devices are just not a viable storage
backend due to the horrific performance vs data integrity tradeoff you have
to make. A physical disk device is the best option, but failing that use 
blktap for file based disks. eg use the tap:aio:/var/lib/xen/images/foo.img
URL scheme for the disk.  NB, if you want good performance with file based
images, regardless of whether using blktap or loopback one should pre-allocate
the entire disk image. Grow-on-demand images are always going to be slow
because every time the host has to grow the image, it hits the journal on
the host filesystem.

Dan.
-- 
|=- Red Hat, Engineering, Emerging Technologies, Boston.  +1 978 392 2496 -=|
|=-           Perl modules: http://search.cpan.org/~danberr/              -=|
|=-               Projects: http://freshmeat.net/~danielpb/               -=|
|=-  GnuPG: 7D3B9505   F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505  -=| 

_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users