virtualizing...

[jarod-ajLrJawYSntWk0Htik3J/w at public.gmane.org (Jarod Wilson)]

On Thu, 2008-11-27 at 08:13 -0500, Stephen Adler wrote:
> Hello all.... My thanks giving day project is to learn about 
> virutalization (beyond vmware) and try and get either KVM or Xen up and 
> running. I've poked around the Internet and in true fashion, there is a 
> lot out there but its hard to digest the first time around. What I can 
> see is that there are two kinds of virtual environments which I'm 
> interested in. KVM or Xen and each can run in paravirtualization mode or 
> full virtualization mode.

Not quite. Xen can run full virt and paravirt. KVM is full virt only.
However, with the aid of xenner (an abstraction layer written by Red
Hat's Gerd Hoffman), xen paravirt guests can run atop KVM.

> From what I can tell paravirt mode needs a 
> modified kernel, but runs faster and full virtualization does not need a 
> modified kernel but runs slower.

Para-virt guests do use a modified kernel, and yes, part of the
modification is to make the kernel aware that its running under a
hypervisor, and optimize critical paths accordingly.

However, the new hotness out there is paravirtualized drivers for fully
virtualized guests -- which is more or less what vmware does. Drop in a
device driver for critical paths like disk I/O, network controller and
video controller, with the device driver optimized with the knowledge
that its running in a virtual guest.

> My plan is to run windows vista in as a guest OS, so I supposed this 
> forces me to use full virtualization(?)

Yes. There are a few paravirtualized windows device driver
implementations out there that can help make it run better too.

> If I want to run a Linux guest 
> OS, then I run a Xen modified kernel as the guest?

You can. But you can also run as a fully virt guest. Personally, I
prefer to just run fully virt linux guests too. (under kvm on my
laptop). Full virt guest performance under kvm is getting quite good.



-- 
Jarod Wilson
jarod-ajLrJawYSntWk0Htik3J/w at public.gmane.org