Re: [Xen-users] Xen 3.4.3 - bad IO performance on drbd devices

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Jul 20, 2010 at 10:46:34AM +0200, Felix Botner wrote:
> Hi everyone,
> 
> i have two servers installed with a debian/lenny based os (64bit), a 
> debian/sid based kernel 2.6.32-xen-amd64 and xen 3.4.3-4. Each server has two 
> drbd devices (protocol c, formatted with ext4) and is primary for one of 
> them. Every drbd pair has a dedicated network interface (a bond mode 0 
> interface with two 1000 Mbps cards).
> 

<snip>

> 
> The io performance on the connected drbd devices is significantly worse if i 
> start the kernel with the xen hypervisor (with "kernel /boot/xen-3.4.3.gz"). 
> Without the hypervisor (but the same kernel) the systems are about 50% 
> faster.
> 

Are you measuring from dom0 or from a guest? 


>
<snip>
> 
> Why is there such a difference?
> Can i optimize my xend (i already added dom0_mem=2048M dom0_max_vcpus=2 
> dom0_vcpus_pin as boot parameter with no effect)?
> Are there any known issues using XEN and bonding/drbd?
> 
> Feel free to ask for more information about the system or the setup.
> 

How much memory does your server have? 
ie. how much ram do you have when you boot it baremetal without Xen.

Remember all the free memory of the host/dom0 will be used by linux pagecache..
So if you limit dom0 to 2GB, it'll have less cache than the baremetal case.

-- Pasi

> Many thanks
> 
> -- 
> Felix Botner
> 
> Open Source Software Engineer
> 
> Univention GmbH
> Linux for your business
> Mary-Somerville-Str.1
> 28359 Bremen
> Tel. : +49 421 22232-0
> Fax : +49 421 22232-99
> 
> botner@xxxxxxxxxxxxx>
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> 
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> 
> 
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