Re: [Xen-users] Disk performance under Xen

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Jul 31, 2009 at 11:59:50AM +0100, Gavin Conway wrote:
> >  Why do you need HVM guest? HVM, aka fully virtualized guests use Qemu
> >  to _emulate_ IDE (or SCSI) adapters and disks, so that'll be slow.
> >
> >  If you can't switch to paravirtual (PV) guests, at least try to
> >  install
> >  PV-on-HVM drivers, which should help a lot. Other possibility is to
> >  use
> >  stubdoms with HVM, but that's not available in Xen shipped in CentOS
> >  5.3.
> >  Stubdoms can be found from Xen 3.4.x
> >
> >  PV guests will be a lot faster, since there's no need for emulation.
> >  I recommend you to run PV guests.
> 
> Hi Pasi,
> 
> We get the same performance under windows but comparing the difference 
> between 
> the two it's easier to demonstrate with 2 x Linux systems. With regards to 
> why we use HVM, 
> this is so we can do P2V migrations of various OS' into Xen.
> 

For windows you should use PV-on-HVM drivers aswell, check the GPLPV drivers.
That way you'll get a LOT better performance.

You can do Linux P2V to PV guest aswell, no need to run HVM.

> Could you link me to the PV-on-HVM drivers for Linux, these sound like a good 
> way forward. 
> Also Stubdoms are a new one on me, do you know of any recommended reading. 
> Googling draws up a blank apart from problems people have had.
> 

http://blog.xen.org/index.php/2008/08/28/xen-33-feature-hvm-device-model-domain/
http://www.xen.org/files/xensummitboston08/SamThibault_XenSummit.pdf

Check those out.

-- Pasi

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