Re: [Xen-users] domU's overloaded

[Tom Brown <xensource.com@xxxxxxxxxxxxxxxxxxx>]

On Sun, 23 Mar 2008, n8&abby wrote:

> I have between 35 and 40 domU's on the same box running the same
> applications and each requiring moderate load.  Each have between 150
> to 512 megs of ram and 50Gb disk space.  These domU's have really
> become sluggish, even adding a large amount of memory helps only a
> small amount.  This may be normal for a system with this many domU's,
> but I'm not really sure how to tell.
>
> Hardware is:
> 1U Acme 5CD16T Xeon 3000/3200 Core 2 Quad
> 4x SATA Drives (domU's are set up with LVM)
> Intel Core 2 Quad Q6600 Quad-Core 2.40GHz 8MB
> 8Gb Ram
So you've got 4 disk drives handling 40 different domUs... that's very 
likely to be your bottle neck, either that or flat out CPU power. If disk 
is your bottleneck, you want to try to find the domUs doing the most disk 
I/O and fix that... or give them more memory if they are doing substantial 
read I/O that might be cacheable. And if you build another server this way 
you might want to buy the fastest drives you can get/afford.
Other than that, no one is really going to be able to tell you much... 
system tuning is so dependent on the applications being run. You need to 
be aware of what your bottlenecks are, develop some tools for figuring out 
how close you are to hitting your limits, and go from there.
tools like "xm list" and iostat will make good starting points. xm list 
gives you cumulative CPU usage, taken over time you can figure out how 
much is spare. iostat will show you which drives are working and to some 
degree, how hard. If you don't have iostat, all the info is in 
/proc/diskstats, but you'll have to write some scripts to parse it. Maybe 
someone else has some better pointers. In my experience, XEN doesn't need 
much tuning itself, but your milage may vary :)
-Tom

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