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Re: [Xen-users] Config difference: Paravirtualization and full virtualiz

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Config difference: Paravirtualization and full virtualization
From: "Ulrich Windl" <ulrich.windl@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 31 Jan 2007 08:10:19 +0100
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On 30 Jan 2007 at 17:55, Jordi Segues wrote:

> Hello,
> 
> I'm playing with xen, but I have a doubt:
> 
> Where's the difference in the guest installation (or maybe in the host
> installation?) when you install a Linux in paravirtualization mode, or
> in full virtualization mode (VT or pacifica)?

Hi!

Did you read about the concepts? Full virtualization should be transparent to 
the 
guest, while paravirtualization requires a special guest. Performance for the 
latter case is usually better.

> 
> I mean, how do you tell to xen that you want to run a linux guest in
> paravirtualization or in full virtualization mode?

As the XEN host (Dom0) provides the guest environment, how should XEN know what 
you want if don't tell it? That is, the guest CAN NOT request a virual machine, 
but the host does provide it.

> 
> And then, can you run a linux (modified to run under
> paravirtualization) in full virtualization mode?

No, because the services offered for paravirtualization by the host are not 
present in full virtualization (AFAIK).

> 
> Can I run a linux in paravirtualization mode and another in full
> virtualization mode, both simultanously?

Would be stupid if you could not: Back in the times of Windows 2.11/386 you 
could 
have multiple DOS boxes in Windows (as opposed to only being able to have one 
on 
OS/2 for 286 CPUs). That's because the 386 hax the virtual x86 mode. It's 
similar 
for the VMX extension.

> 
> Thanks a lot!
> And sorry if this is a basic question.

If XEN had a proper concepts guide, I'd refer you to that.

Ulrich


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