UML vs. vserver vs. xen

[Fraser Campbell]

Daniel Armstrong wrote:

> What I want to do:
> 
> - make use of a single server (Athlon XP +1800, 512MB RAM)
> - use debian 'stable' as the base install
> - use same version of debian for all the 'virtual' machines as well
> - a single admin (me)
> - no X server required
> 
> Right now I am leaning towards the vserver option, as this way all the
> virtual machines make use of the single underlying kernel and I would
> think this makes a lighter demand on this older hardware as opposed to
> UML or xen, where every virtual machine has its own kernel. The
> trade-off is in robustness - if something goes wrong with your kernel,
> all your virtual machines are hosed.
> 
> Anybody have any experience with the above-mentioned solutions and
> opinions to share? Or should I just keep it simple and have a single
> server that implements everything required?

If you want to do this as a learning exercise then I think it's 
definitely worthwhile.  Virtualization is a huge trend and knowing it 
inside and out will be very beneficial for you if you work in IT.

Practically speaking I don't see a big advantage to any virtualization 
at home if you're going to run the same OS in each VM.  Where I expect I 
will use it at home is to run Debian + Ubuntu + SLES + RHEL + ?  Dual, 
triple, quad booting is a PITA, Xen makes it a little more manageable 
without much overhead.

My opinion is that UML is a nice technology but it is likely to lose 
favour now that Xen is available.

Vservers is a different approach to virtualization also a neat 
technology.  Down the road I wouldn't be surprised if a combination of 
Xen + vservers might even come into play.  Another solution similar to 
vservers is OpenVZ from SW Soft.  The "open" part is a very recent 
development though their commercial product (Virtuozzo) has been around 
for a long time.

I haven't seen the issues that Adam mentioned with Xen.  I have done a 
lot of benchmarking between Xen Linux, native Linux and Linux on VMWare 
ESX.  Xen Linux performance is very good, close to native as advertised. 
  My benchmarking has only gone up to 4 VMs so far but the degradation 
in peformance was not significant and definitely not noticeable to the 
point where the console slowed down. My initial benchmarking was on 2 
way servers with 4GB RAM, we're just starting to look at 4 way servers 
with 8GB of RAM as of today ;-)

If you haven't tried the Xen Demo CD you should take a look, worked like 
a charm on my laptop ... 3 operating systems running with full graphical 
desktop (via VNC) and flawless networking in 512 MB of RAM from a live CD.

My $0.02!
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