[linux-lvm] clvm, snapshots and live migration

[Dietmar Maurer]

Hi all,

I started this thread on the wrong (cluster-devel) mailing list. So I post it in
the linux-lvm list to correct that mistake:

> > We use clvm and store VM images on shared storage, and our backup tool
> > uses LVM snapshots, which seems to require that we exclusively lock the LVs.
> >
> > But live migration requires that we activate the LVs on two nodes, so this
> conflicts with exclusive locks.
> >
> > So is there a way to convert the exclusive lock into a local lock. I get an error
> when try that.
> >
> > For example:
> >
> > First acquire an exclusive lock:
> > # lvchange -aey vmdisks/vm-102-disk-1
> >
> > I now want to change that into an local lock:
> >
> > # lvchange -aly vmdisks/vm-102-disk-1
> >   Error locking on node proxmox-7-60: Device or resource busy
> >
> > Is there a way to do that? What is the reasoning behind not allowing that?
> 
> Not actually an answer.
> After migration you'd need to convert lock opposite way.
> One problem I see here is that if we upgrade local lock to exclusive, then we
> need either to force other nodes to drop their local lock unless LV is used or just
> fail.

Yes - the idea is that the migration tool release the lock on the other node.

So after migration only the target node holds a local lock, and we can upgrade
that lock to exclusive without problems.

> Probably lvm list is a better place for such discussions?

Sure, you are right (just noticed that I posted to the wrong list).

- Dietmar