Re: [linux-lvm] resize and snapshots with clvm

[Jacek Konieczny <jajcus@jajcus.net>]

On Wed, 20 Feb 2013 14:18:23 +0100
Andreas Pflug <pgadmin@pse-consulting.de> wrote:
> I would have expected lvm to take that exclusive lock implicitely
> when necessary?

I would not expect that. LVM provides means to activate in a shared or
exclusive way, but it does not choose itself.

> > When the LV is exclusively activated (lvchange -aey) snapshots
> > should work (and they do work for me).
> 
> The volume is "lvchange -aly" active on one node and in use there
> (e.g. mounted or attached to a VM). If I try to lvchange -aey on that
> node, I get "Error locking on node xxxx: Device or resource busy".

I do not use '-aly' (in fact I am not sure what it does), so I cannot
relate.

> Actually, lock exclusive will even fail if the device is not in use,
> but only active locally.
> 
> A workaround would probably be to activate the lv exclusively
> _before_ using it, but then it would be impossible to migrate the vm
> to another host later on.

I use clustered LVM for my VMs too and always use "-aey" locking mode –
each volume can be active on a single cluster node a time. When doing VM
migration I first deactivate the volume on one host, then activate
it (exclusively) on the other. I feel safer knowing none of the volumes
will ever be active on more than one host.

Is your scenario much different?

Greets,
	Jacek