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Re: [Xen-users] xen-on-xen

To: xen-users <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] xen-on-xen
From: Jeff Lane <sundowner225@xxxxxxxxx>
Date: Tue, 3 Mar 2009 12:31:47 -0500
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On Mon, Mar 2, 2009 at 9:23 AM, Heli <helicoterus-elih@xxxxxxxx> wrote:
> An hypervisor is able to run in a virtual machine if hypervisor construction
> and copmuter architecture meet the second Popek's and Goldberg's theorem
> (about recursive virtualization).
> Xen does not meet it, because x86 architecture is not a "perfect"
> virtualizable one.

As has been said... yes you can.  It's not pretty, and certainly not
recommended.  I've done it before using RHEL 5 and Xen running an
additional RHEL 5 HVM guest with Xen in that.  It's certainly ugly,
and incredibly slow, but you can at least log in and use it.

Now, that being said, would I try that "in the real world": absolutely not.
Would I use that in your case of testing customer backups: No way...

Sure it works, but it doesn't work well, and I would not trust that to
verify a customer scenario.  Best bet would be for you to buy a couple
spare servers and use those to verify Xen... hell, charge the customer
an extra fee for the hardware required to verify their backups, if you
can.

For what it's worth, I HAVE gotten this to work before:

RHEL 5 / Xen Host -> RHEL 5 /Xen HVM guest -> rhel 5 PV domU

And like I said, it was UGLY, and barely usable... but at least in the
abstract sense, it does work... :-)

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