[Wolves] Linux Virtual machines

[David Goodwin]

<snip>
> Qemu requires a GUI, afaik; it's good for vmware sorts of things, but
> it's destined more towards running stuff you need to see than to
>

man qemu provides the following :

-nographic
 Normally, QEMU uses SDL to display the VGA output. With this
 option, you can totally disable graphical output so that QEMU is a
 simple command line application. The emulated serial port is redi‐
 rected on the console. Therefore, you can still use QEMU to debug a
 Linux kernel with a serial console.

Qemu (and others like vmware) have the advantage that the guest O/S does
not (and is not) aware of the fact that it's virtualised - therefore you 
run things like Windows, Solaris, BSD etc etc under Qemu.
Because they are virtualising at such a low level they tend 
to be much slower than e.g. Xen, although they do often have kernel modules
which attempt to compensate for their sloth-ful-ness.

Xen has the problem that at the moment, the guest O/S needs to be aware 
that it's in a Xen environment (this allows Xen better performance, 
amongst other things). With the arrival of new chip technology (AMD's 
Pacifica (Intel have something similar)) it will be possible to 
virtualise the O/S At the CPU level, which will mean the guest OS will 
not need to be aware it's running under e.g. Xen, and good performance 
will be obtained. This will mean that you will be able to run Windows 
under Xen on a Linux host with minimal overhead.

UML is a Linux only virtualisation, which has limited scope for usage 
(I think it's only been popular as it pre-dated e.g. Xen, is free, and has 
been used by people like Bytemark quite successfully). I get the impression
that everyone (!) will probably move from UML to Xen in the near future
due to the performance benefits and the greater community around Xen.
(I've indirectly had the impression that UML is slowly fading away, but 
I've not really attempted to verify this... perhaps it's just that Xen
has had all the press lately).


(Please note: I'm no virtualisation expert, this is just a sort of 
regurgitation of a Xen talk I saw at UKUUG. My memory is not very reliable.)

Thanks
David.

--
David Goodwin
w: http://www.clocksoft.co.uk 
e: david.goodwin at clocksoft.com
t: 0121 313 3850