Re: [Xen-users] How can I duplicate a running guest OS in Xen ?

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

Tim Post wrote:
> On Sat, 2007-04-28 at 09:58 +0800, openbsd shen wrote:
>   
> > When a guest OS is running in Xen, how can I duplicate it?
> > Thanks.
> >
> > Sailer
> >     
> There is no "elegant" way to do this if the guest is running. The best
> way I've found is to follow these steps :
>
> 1.) On dom-0 create a vbd of equal size (or the size you want for your
> clone). This can be a loop, lv , whatever.
>
> 2.) xm block-attach it to the running dom-U
>
>   
Use rsync on the live OS to push to a mounted partition of another OS. 
Be sure to exclude /proc, /sys, and similar mount run-time created 
directories, and manally push things like /dev/null and /sev/serial that 
reside under the udev created countents of /dev/ For databases which 
cannot safely be duplicated while live, exclude them from the push and 
use tools like mysqldump to dump them to pushable text files.
I use this technique to create nightly backup snapshots with "rsnapshot" 
for recovery purposes. Works pretty well!
> 3.) Enter the dom-u, most likely you will have to use mknod to create
> the device for the new drive in /dev (probably going to be sdc1 if its a
> pv guest) in which case you'd type 'mknod /dev/sdc1 b 8 33' 
>
> 4.) Format it (this can also be done on dom-0) and mount it.
>
> 5.) Use rsync or a similar utility to make a copy of the root file
> system. Get only the stuff you need.
>
> 6.) Once copy is done, unmount the second fs, 'sync' and exit the dom-u
>
> 7.) Go to dom-0 xm block-detach the cloned drive. create your config for
> the new VM, make a swap vbd for it, get it all set up. Mount the file
> system in dom-0 and make your edits in etc/ to change networking (ip and
> stuff)
>   
That's where I do the rsync stuff one final time, with the shutdown and 
manually mounted filesystem. This also avoids the target having to be 
the same size or even set up with the same filesystems. Or if the target 
need not be absolutely identical, such as slave copies of master 
servers, it allows in-vivo operations to preserve configurations of the 
slave.

> 8.) Unmount and boot the new clone :)
>
> Like another poster has said, if your current dom-u is under heavy
> stress (lots of SQL activity or so) this isn't the best idea even using
> the above method which doesn't need to worry about locking. You still
> should watch inodes like you would in any other regular GNU/Linux
> system.
>
> If you are running database servers, you should dump -> import them from
> old to new after booting the clone so that they're identical. Lots of
> stuff could have changed after rsync left /var/lib.
>
> Hope this helps, 
> --Tim
>   
And you should be dumping them regularly as part of backup and recovery 
techniques.
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