Re: Using xen and drbd/migration

[daniele patoner <daniele.patoner@biblio.unitn.it>]

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 
> 
> 
> 
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