XEN questions

Rakhesh Sasidharan rakhesh at rakhesh.com
Mon Jul 30 05:15:14 UTC 2007

> Does one run XEN inside of freebsd and then VMs inside that, or does
> one run XEN on the bare hardware and then run freebsd inside that?  If
> I've already got freebsd running on my box, do I have to reload it
> from scratch or is there a way I can virtualize what I already have
> runing?


Xen runs on the bare hardware and other OSes run atop Xen (i.e. they are
specifically "ported" to the Xen "hardware"). But you don't have to
install Xen on the bare hardware as such. Typically you install Xen on
your OS. And then you install other OSes on this Xen installation. That's
how it works.

For example: Say you are running FreeBSD 7.0. You install Xen on FreeBSD
7.0. Then you install FreeBSD 6.2 and NetBSD 3.1 onto Xen. In Xen
terminology, all these OS installations (including the FreeBSD 7.0 on
which Xen is installed) are called "domains". The FreeBSD 7.0 Xen domain
is called dom0 (domain 0). While the FreeBSD 6.2 and NetBSD 3.1 Xen
domains are called domU (domain User).

dom0 is special coz that's what manages the other domains. Plus, that's
where you install Xen first for it to interact with the hardware etc. Not
all OSes support Xen on dom0. FreeBSD 6.2, for instance, doesn't. (It only
supports domU). FreeBSD 7.0 would, I believe. NetBSD 3.1 does. In Linux,
you need kernel 2.6.18 and greater I think.

So to answer your question, if you are on FreeBSD 6.2, you can't try out
Xen. You can, however, install FreeBSD 6.2 atop any Xen installation
running on FreeBSD 7.0 and Linux or NetBSD 3.1 etc.

Hope this helps. :)


ps. This should be of some info --

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