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Re: [Xen-devel] poor I/O performance on domU

Anthony Liguori wrote:
On Sat, 2005-01-15 at 08:36, Jan Kundrát wrote:

Anthony Liguori wrote:
yes, dom0 filesystems are on partitions located on hda.


My theory is that since hda is a single disk if you've got dom0 reading
and writing to it and another partition reading and writing to the same
disk at the same time both are going to be slower than if you were just
writing to hda on dom0.

OK, I'll try to add another device and play with it. BTW, both dom0 and the domain<n> (running ttylinux) was idle, almost without disk activity. I just run `hdparm` inside dom0, waited for results, dtto in domainU, and repeated several times.

That's why I suggest trying it with a neutral device.


I've tried exporting /dev/hda7 (not used neither mounted from dom0) as sdb7 and I can get about 12.3 MB/s. From dom0 I get about 14.8 MB/s.


That seems pretty reasonable. Doesn't seem like there's a problem. Sharing partitions between dom0 and domU seems like a bad idea. Look
through the threads in the list about filesystem corruption.

30% performance loss seems like a problem for me ;-), comparing to <3% (iirc) in xen's benchmarks. I just want to find out if the problem is in Xen.

Of course I'm *not* sharing the same partition between domains, I'm only performing read benchmarks on the same disk location.

-jkt

--
cd /local/pub && more beer > /dev/mouth



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