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

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

>
> We haven't tested 3.1 enough to know if this is still a problem.  If it
> is important to gather this information for 2.0.7, I'll do so and submit
> it.  Please let me know so I don't spend the time unnecessarily.  If it
> will be helpful, I most gladly try the dd and figure out what scheduler
> we ultimately used.  Thanks - John

To be honest, for 2.x I don't think it'll be worth your time: it's too out of 
date and development has moved on a longer way...  I don't think anybody is 
going to fix anything Xen 2 based.  Sorry :-(  I guess Xen isn't a big enough 
project to have an "old stable" patching scheme as the Linux kernel does.

But if you observe worrying performance behaviour on 3.x please do report it.  
Doubly so if it's a regression wrt Xen 2.  I'll have my fingers crossed that 
your problems are resolved under Xen 3.1.

By the way, remember that if you need to run legacy virtual machines e.g. 2.4 
you could run them in HVM mode on Xen 3 (if your hardware supports it).  I 
believe there are even some paravirtualised drivers around for 2.4 Linux that 
you could use to boost IO performance in HVM.  Actually, you could run the 
entirety of Xen 2.x and its guests in HVM mode, but this probably wouldn't do 
much for the IO performance (and there would quite likely be problems 
compiling optimised drivers for it!).

Good luck with it anyhow.  Hope you find that Xen 3 is to your liking; there 
are lots of cool features there.  If you don't have a requirement to run 
less-common OSes (e.g. NetBSD, Plan9 etc) I'd suggest that you try to use 
PAE-enabled 32-bit guests under Xen 3.  This will enable you to migrate them 
more easily to a 64-bit Xen at a future date.

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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