Using xen and drbd/migration

Using xen and drbd/migration

[Michael Paesold]

Hello,

short introduction, my name is Michael Paesold, I am student from 
Austria/Europe and I am currently evaluating high availability and 
virtualization technologies for Linux/Unix.

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?

If no, I think a way would be to implement a module interface for the 
migration so that one can setup the environment after the VM is stop, but 
before the VM is resumed on the new host.

Ideas?

Best Regards,
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

Re: Using xen and drbd/migration

[daniele patoner]

I have successfully migrated domU with gnbd, but with a third host C that
export the root filesystem, but IMHO support for drbd is a nice feature 
for  High-Affidability  purpose with xen.

http://sources.redhat.com/cluster/gnbd/gnbd_usage.txt


Daniele

Michael Paesold wrote:
> Hello,
> 
> short introduction, my name is Michael Paesold, I am student from 
> Austria/Europe and I am currently evaluating high availability and 
> virtualization technologies for Linux/Unix.
> 
> 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?
> 
> If no, I think a way would be to implement a module interface for the 
> migration so that one can setup the environment after the VM is stop, 
> but before the VM is resumed on the new host.
> 
> Ideas?
> 
> Best Regards,
> 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 
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>