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Re: [Xen-users] Re: Xen Disk I/O performance vs native performance:Xen I

To: "Fajar A. Nugraha" <fajar@xxxxxxxxx>
Subject: Re: [Xen-users] Re: Xen Disk I/O performance vs native performance:Xen I/O is definitely super super super slow
From: Joris Dobbelsteen <joris@xxxxxxxxxxxxxxxxxxxxx>
Date: Sat, 14 Feb 2009 14:47:01 +0100
Cc: xen-users <xen-users@xxxxxxxxxxxxxxxxxxx>, DOGUET Emmanuel <Emmanuel.DOGUET@xxxxxxxx>
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Fajar A. Nugraha wrote, On 14-02-09 06:22:
2009/2/13 DOGUET Emmanuel <Emmanuel.DOGUET@xxxxxxxx>:

I have mount domU partition on dom0 for testing and it's OK.
But same partiton on domU side is slow.


Strange indeed. At least that ruled-out hardware problems :)
Could try with a "simple" domU?
- 1 vcpu
- 512 M memory
- only one vbd

this should isolate whether or not the problem is on your particular
domU (e.g. some config parameter actually make domU slower).

Your config file should have only few lines, like this

memory = "512"
disk = ['phy:/dev/rootvg/bdd-root,xvda1,w' ]
vif = [ "mac=00:22:64:A1:56:BF,bridge=xenbr0" ]
vfb =['type=vnc']

I has one read somewhere that it could be caused by an interaction between LVM and Software RAID. You should break up your test into smaller fractions:

* Plain disk (NO RAID OR LVM)
* RAID only
* LVM only

Maybe this isolates the issue a bit. I'm also strugling with similar numbers for disk performance, but since I run all my network services on top of one Xen box (personal system, not business) I have little intention to actually change it now. Its running an outdated Gentoo installation (upgrade attempts broke Xen in my case).

My memory might have failed after a year, but I believed that without RAID or LVM the performance was equal in both Dom0 and DomU.

- Joris

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