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

[Felix Botner <botner@xxxxxxxxxxxxx>]

Am Dienstag 20 Juli 2010 14:35:30 schrieb Pasi Kärkkäinen:
> 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?

From dom0, there are no guests at the moment.


>
> > 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.

~20GB without Xen. Now i removed the hypervisor param dom0_mem=2048M from 
menu.lst (in xend-config set (dom0-min-mem 196) and (enable-dom0-ballooning 
yes)), rebooted and as far as i know there should be no memory restriction 
for dom0. "xm list" shows me the complete memory for dom0:

server1-> xm list
Name                                        ID   Mem VCPUs      State   
Time(s)
Domain-0                                     0 18323     2     r-----   1785.0

server2-> xm list
Name                                        ID   Mem VCPUs      State   
Time(s)
Domain-0                                     0 22375     2     r-----   1754.2

But bonnie++ gives me still bad results:

server1,60000M,,,113444,30,55569,13,,,231555,23,622.6,0,16,25634,70,+++++,+++,
+++++,+++,+++++,+++,+++++,+++,+++++,+++
server2,60000M,,,114014,31,53864,13,,,243541,27,617.4,0,16,+++++,+++,+++++,
+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++

So i don't think caching is the issue, or?

bye

Felix

>
> 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>
> > http://www.univention.de
> >
> > Geschäftsführer: Peter H. Ganten
> > HRB 20755 Amtsgericht Bremen
> > Steuer-Nr.: 71-597-02876
> >
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-users


-- 
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>
http://www.univention.de

Geschäftsführer: Peter H. Ganten
HRB 20755 Amtsgericht Bremen
Steuer-Nr.: 71-597-02876 

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