Re: [Xen-users] Disk performance under Xen

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Jul 31, 2009 at 11:32:53AM +0100, Gavin Conway wrote:
> Hi All,
> 
> We're seeing some really poor disk performance under Xen Source. 
> Below are the output of some Bonnie++ tests ran on the underlying host 
> as well as on a HVM instance. We've seen the same level of performance 
> on Debian Etch and Debian Lenny. Can anyone comment on what we might do 
> to improve this and get near-native performance from a HVM machine.
> 

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.

-- Pasi

> 
> 
> Host - Running Centos 5.3
> 
> Version  1.03       ------Sequential Output------ --Sequential Input- 
> --Random-
>                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
> --Seeks--
> Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec 
> %CP
> tig-xen-host-1. 14G           212037  38 115111  19           300545  12 779.4
> 
> Write: 207MB/s
> Rewrite: 112MB/s
> Read: 293.5MB/s
> 
> 
> Guest host - running Centos 5.3
> 
> Version  1.03       ------Sequential Output------ --Sequential Input- 
> --Random-
>                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
> --Seeks--
> Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec 
> %CP
> localhost.locald 2G           29566   4 21399   5           88812   9 497.7   
> 6
> localhost.localdomain,2G,,,29566,4,21399,5,,,88812,9,497.7,6,,,,,,,,,,,,,
> 
> Write speed: 28.87MB/s
> Rewrite speed: 20.89MB/s
> Read: 86.73MB/s
> 
> 
> Thanks
> Gavin
> 
> 
> 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
> This email must be read in conjunction with the legal & service notices on 
> http://www.uksolutions.co.uk/disclaimer
> 
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