Re: [Xen-users] XEN 3.1 on 2.6.18-164.el5xen kernel - Slow IO & Pauses

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Sat, Nov 7, 2009 at 2:55 AM, Robert Taylor <rob@xxxxxxxx> wrote:
> I've seen tons of posts about slow IO under Xen and others without slow IO
> under xen.   Here's what I'm experiencing.   I've got a XEN system on an 2
> dual core AMD Opteron 275 processors.
>
> I'm running DRBD for disk, but have also tested without DRBD.
> Throughput in Dom-0 seems to be 50-80MB/sec for a file of any size.
> Throughput in DomU is 20-30MB/sec for a file under 2GB, and 1-2MB/sec for
> a larger file.

How do you measure the throughput?

> Any help would be appreciated.  This is under CentOS 5.4, 8GB memory, 1TB
> SATA nv-sata controller.   Tyan K8SRE S2891 motherboard.   NVidia nForce
> 4Port SATAlink controller.

I'm using a similar software setup (RHEL5), different hardware though.
I'd suggest you start with doing "iostat -mx 3" on both dom0 and domU
to see where the bottleneck is. My guess is that some process is using
lots of I/O (possibly in small sizes) so that you're practically IOPS
bound, and the problem is not directly related to Xen.

-- 
Fajar

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