[Cluster-devel] clvm, snapshots and live migration

[Cluster-devel] clvm, snapshots and live migration

[Dietmar Maurer]

Hi all,

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?

- Dietmar

[Cluster-devel] clvm, snapshots and live migration

[Vladislav Bogdanov]

Hi,

24.11.2011 13:42, Dietmar Maurer wrote:
> Hi all,
> 
> 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.

Probably lvm list is a better place for such discussions?

Vladislav

[Cluster-devel] 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