Re: [tlug] xen and windows

["Mike Mazur" <mmazur@example.com>]

Hi,

On 10/14/07, Simon Cozens <simon@example.com> wrote:
> Mike Mazur wrote:
> > When I looked into Xen I discovered that you have to assign a certain
> > portion of your RAM to your "host OS" (dom0 in Xen terminology[1]) at
> > boot time, with the remainder left for your guest OSs when they start
> > up. This means when I have no VMs running, a chunk of my RAM is
> > inaccessible.
>
> This is completely untrue, and completely confused.

Well, it wouldn't be the first time :)

> You're using vmware concepts ("host OS", "guest OS") when discussing
> Xen, which doesn't use those concepts. But even in doing so, you take an
> argument that would be crazy in VMWare ("My host OS requires RAM to run!
> How bad is that!") and apply it in Xen; it doesn't make any more sense
> there either.
>
> dom0 is not a host OS; dom0 is a privileged domain. You can't usefully
> have "no VMs running" with Xen. If you completely ignore your dom0, then
> yes, it's a waste of RAM. So don't do that.
>
> dom0 is your first "guest OS". Xen is your "host OS". Now Xen itself
> takes a bit of RAM to operate, I'll grant you, but that's an unfortunate
> artifact of actually using any non-trivial software.

I guess what I understood from Xen is that you configure how much
memory your dom0 instance uses. If your intention is to run other VMs
alongside your dom0, you cannot allocate all your RAM to the dom0
instance. This means that even if no other doms are running, your dom0
will not use all the currently available memory.

In my case, I use other VMs only occasionally, so such an arrangement
doesn't work for me.

Maybe I should give the Xen documentation a more thorough read, though.

Sorry about the confusion :)
Mike