[ClusterLabs] Antw: VG activation on Active/Passive

[Jorge Fábregas]

On 08/31/2015 02:41 AM, Ulrich Windl wrote:
> Actually when using ext3 I wouldn't use cLVM, so this variant 
> wouldn't exist then.

Hi Ulrich,

I tried it first without cLVM (so I could get rid of DLM as well) but
then you have to modify /etc/lvm/lvm.conf accordingly. You have to
activate the "volume_list" option and exclude from it the VGs that are
going to be used on the cluster.  If you don't activate the option
(which is commented by default) the LVM resource agent is going to
complain (it's just a precaution).  As a consequence of enabling that
option you're not allowed to manually perform operations on the VG
(lvextend etc) while the cluster is running.  In the end it turns out
using cLVM was easier....

> I see the danger that someone might mount the ext3-LV in a second
> node by mistake. Sometimes this will corrupt the filesystem in a way
> that fsck cannot repair, and maybe you'll discover that days after it
> happened...

Now with cLVM....when using the LVM resource agent (which activates the
VG) there's an option to activate it *exclusively*; therefore the VG is
only active on the node where the LVM resource is running.  On the other
node the VG isn't activated and therefore you won't even have the
logical-volume device-files created (to even try to mount it).  You may
manually perform "vgchange -a y myVG"  (in order to try to activate it
and create the device-files) to active it but it fails to do so (wisely).

Regards,
Jorge