[DRBD-user] DRBD, Xen, HVM and live migration

Bart Coninckx bart.coninckx at telenet.be
Fri Sep 23 18:13:15 CEST 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On 09/23/11 12:29, Felix Frank wrote:
> Hi,
> On 09/23/2011 11:09 AM, Bart Coninckx wrote:
>> Hi all,
>> What would be a good strategy these days to accomplish this on a two
>> node system (no external storage)?
> A simple LVM ->  DRBD ->  Guest Partitions approach has worked fine for me.

So how do you live migrate? Are they both primary?

>> Do I need to complexity of a clustered filesystem?
> Where would that come into play? Are you thinking of using disk image
> files for your guests? That sounds icky.

Yes. I was thinking that if you need dual primary for live migration you 
would also need a clustered file system (and thus images, mind you I'd 
rather stay away from them too ...).

>> Could I throw LVM snapshots for backup somewhere in the mix too?
> Absolutely. But then, you can just sever the replication link and end up
> with a "free" unchanging image on the Secondary.
> Don't let your primary crash at that time, though - snapshots should add
> more safety.

right, but suposse I do an "xm save" first, snapshot, and then xm 
restore, all is well, right?

>> I looked at http://www.drbd.org/users-guide/s-xen-configure-domu.html ,
>> but this seems to exclude HVM guests.
> I think it's a good option to have Xen use the DRBDs as plain block
> devices, i.e., Xen doesn't need to be aware of DRBD.
> I believe I read on this list that live migration is quite possible so
> long as both nodes become primary on time.

The getting "primary" on time is somewhat mistifying to me, especially 
in the context of Pacemaker, but that is probably another question for 
another mailing list.

thx Felix!


> HTH,
> Felix

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