[Xen-users] Using xen and drbd/migration

["Michael Paesold" <mpaesold@xxxxxx>]

Hi,

I have first written to xen-devel with this question, but this list is 
probably more appropriate.
----- previous message

What I want to do is to use xen with a drbd[1] device as root for a domU
and then be able to migrate the domU between two host systems. I have
already read the documenation on xen and some papers[2] and searched
through the archives about drbd/xen usage. Unfortunatly my questions are not 
covered anywhere, so I hope you can help me.
drbd would run in the domain 0 to replicate a block device,
say /dev/drbd0 on host A and host B. Xen would be set up on both hosts.
On host A I would create a new VM with /dev/drbd0 as root.

drbd will now sync /dev/drbd0 from host A to host B and keep those two
consistent. Nevertheless in a drbd setup only on host can be primary and
only one host may access a device (read/write).

So a live migration of a VM from host A to B would have to look like
this:

pre-copy migration
suspend VM on A
stop-and-copy phase
--> on A: drbdadm secondary drbd0 # make A secondary for /dev/drbd0
--> on B: drbdadm primary drbd0 # make B primary for /dev/drbd0
resume VM on B

(with the root now pointing to the local /dev/drbd0 device)

Is there a way to do this with xen 2.0 or 3.0?

----- previous message end

Now what I have found going through the source/example files is that the 
block- scripts could be used to setup drbd. I would have to create a 
block-drbd script supporting bind/unbind of a drbd device.
Does this sound resonable with the requirements described above?
Btw. I am willing to help provide documentation for xen/drbd if this works 
out for me. This could help other people, too.
Thanks for answers.

Michael Paesold

[1] distributed remote block device - http://www.drbd.org/
[2] e.g.
http://www.cl.cam.ac.uk/Research/SRG/netos/papers/2005-migration-nsdi-pre.pdf



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