[Xen-users] Questions before starting an interesting Xen project

[Rickard Borgmäster <doktorn@xxxxxx>]

Hello,

Me and four other students at Royal Institute of Technology (KTH) in 
Sweden are in the startup phase for an interesting project utilizing 
Xen. We have been asked to modernise and improve the performance of a 
router simulation package called Crab[1]. Currently Crab runs a few 
instances of UML and inside each guest OS Quagga[2] is run. Quagga is a 
routing daemon with interface similar to Cisco's IOS. This package gives 
students the opportunity to boot a LiveCD in their computer and get 
instant access to a virtual environment of a bunch of routers. The 
students can exercise Cisco CCNA/CCNP level studies without actually 
having the hardware.
Our task is to replace UML with Xen for this solution.

I think this Xen is a very interesting software and this project is very 
well suited to be run under Xen.
During a learning process questionmarks pop up constantly. While reading 
docs, mailinglists and such, some of them are straightened out and some 
even become multiplied. Some of the latter I will post here to see if 
the Xen community will help me straighten these out.
let's go :-)

* Minimum kernel/memory usage for domU
The goal with this solution is to enable students to run as many virtual 
routers (using Quagga) as possible within the same computer. Therefore, 
the memory usage inside domU needs to be minimized. Using the demoCD 
2.0.6, I found out that 19MB ram were used after all services and 
running processes were stopped. Is this the absolute minimum or is it 
possible to reclaim further more memory? Is the ramdrive actuallty 
needed? If so, how small can I push it?
* Memory required for dom0
Is there a formula or so for calculating dom0 memory requirement? Ie 
some base amont + constant * number of domU's? If we can "afford" it, a 
GUI with X would be nice, so that students can read an online manual in 
a web browser while having console windows to the domU's running routing 
daemons.
* Capacity
If we succeed in optimizing the environment well, how many virtual 
machines would be possible to run in a 256MB ram machine?
* dom0 and domU kernels
What kernels do you recommend for dom0 and domU? Some specific distros 
or kernels optimized for maximum memory efficiency?
* Other limiting factors
Right now memory is the limiting factor as far as I can understand. 
Beening new to this, I most likely missed something. What other factors 
must I calculate with for capacity planning? I think the goal is to run 
somewhere around 10 domU's.
Hope to hear from you all. If anyone has ever heard or read something on 
the 'net about a similar solution, I'd be really glad to hear about it.
Best regards
Rickard Borgmäster

[1] http://www.isk.kth.se/proj/crab/
[2] http://www.quagga.net/


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