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List:       xen-users
Subject:    Re: [Xen-users] migrating to xen (newbie question)
From:       Simon Hobson <linux () thehobsons ! co ! uk>
Date:       2010-04-30 6:52:20
Message-ID: p06240871c8002c0431ba () simon ! thehobsons ! co ! uk
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Miles Fidelman wrote:

>I'm sure this has been asked before, but I can't seem to find an answer:
>
>I have a production system running on a plain vanilla Debian 
>environment.  I'd like to migrate everything into a DomU running on 
>top of Xen.
>
>Is there a simple (or at least well defined) way to take a snapshot 
>of a system and turn it into an image that can be run virtualized?

It's something I've done myself several times. To run as a PV guest 
(PV=Para Virtualised = guest is modified to co-operate with host) 
then you need to be running a Xen PV guest capable kernel. Some 
distros now ship with PV capable kernels as default, but older ones 
don't.

If you can afford to modify the running system, then install a new 
'-xen' kernel before you do anything.
Create the container(s) for your virtual disks on the host - my 
preference is one LVM volume per guest volume. Create the 
filesystems, and mount them on the host.
Copy all the files from your running system to the mounted filesystem 
on the host - my preference is to use rsync (don't forget the 
--numeric-ids option !) Doing it this way means you can run it once 
with the system live, shutdown all the services (such as databases) 
that need to close files, and run the copy again to get the handful 
of files up to date.
You can now modify /etc/fstab, /etc/network/interfaces (or the 
equivalent on your distro) before unmounting the filesystems from the 
host and shutdown the original machine before starting the guest VM.

IFF you got all the above steps right, then the guest should start.

If you aren't able to modify the running system, then you can chroot 
a session on the host and install the new kernel there before you 
unmoun the guest filesystems. I've done that, got loads of warnings - 
I assume due to the running kernel/environment not being the same as 
the guest I'm modifying.

-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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