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RE: [Xen-users] Disk performance under Xen

To: 'Pasi Kärkkäinen' <pasik@xxxxxx>
Subject: RE: [Xen-users] Disk performance under Xen
From: Gavin Conway <gavin.conway@xxxxxxxxxxxxxxxxx>
Date: Fri, 31 Jul 2009 11:59:50 +0100
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Thread-topic: [Xen-users] Disk performance under Xen
>  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.

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.


Gavin Conway
Senior Engineer, Operations (Systems Group), UKSolutions

Telephone: 0845 004 1333, option 2
Email: gavin.conway@xxxxxxxxxxxxxxxxx
Web: http://www.uksolutions.co.uk/
UKS Ltd, Birmingham Road, Studley, Warwickshire, B80 7BG Registered in England 
Number 3036806
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