Re: [Xen-users] disk performance about half in domU? + question about XenSource

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Based on some tests we ran, it seems the biggest performance
> hit you get from running within domU is from disk I/O. We
> did some mysql read and write tests, and for both, our
> performance is about half that compared to native. Has that
> been others' experience?
>
> Is there any way to make this better? We are using physical
> partitions. In contrast, cpu/memory tests appear to be near
> native.

Sounds a bit weird.  How many CPUs in this box?  My memories of the benchmarks 
suggest this should be better than you're seeing, but maybe your workload is 
tickling some bad cases or something...

I know this sounds really weird but when comparing to native performance you 
do need to test on the same area of the disk, have you done this?  Portions 
of the disk nearer to the outside edge of the platter can have significantly 
higher transfer rates due to moving at a higher linear velocity.

> Does buying commercial Xen (XenSource) help in anyway? Do
> they have optimized disk drivers?

XenEnterprise and friends add optimised disk drivers for Windows, but if 
you're running paravirtualised Linux then you've already got optimised disk 
drivers, so the commercial product probably won't help.

Cheers,
Mark


-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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