On Tue, May 14, 2013 at 11:36:54AM -0400, David Vossel wrote:
> ----- Original Message -----
> > From: "Lars Ellenberg" <lars.ellenb...@linbit.com>
> > To: "Lars Marowsky-Bree" <l...@suse.com>
> > Cc: "Fabio M. Di Nitto" <fdini...@redhat.com>, "General Linux-HA mailing
> > list" <linux-ha@lists.linux-ha.org>,
> > "Jonathan Brassow" <jbras...@redhat.com>
> > Sent: Tuesday, May 14, 2013 9:50:43 AM
> > Subject: Re: [Linux-HA] LVM Resource agent, "exclusive" activation
> >
> > On Tue, May 14, 2013 at 04:06:09PM +0200, Lars Marowsky-Bree wrote:
> > > On 2013-05-14T09:54:55, David Vossel <dvos...@redhat.com> wrote:
> > >
> > > > Here's what it comes down to. You aren't guaranteed exclusive
> > > > activation just because pacemaker is in control. There are scenarios
> > > > with SAN disks where the node starts up and can potentially attempt to
> > > > activate a volume before pacemaker has initialized.
> > >
> > > Yeah, from what I've read in the code, the tagged activation would also
> > > prevent a manual (or on-boot) vg/lv activation (because it seems lvm
> > > itself will refuse). That seems like a good idea to me. Unless I'm
> > > wrong, that concept seems sound, barring bugs that need fixing.
> >
> > Sure.
> >
> > And I'm not at all oposed to using tags.
> > I want to get rid of the layer violation,
> > which is the one Bad Thing I'm complaining about.
> >
> > Also, note that on stop, this strips all tags, leaving it untagged.
> > On the next cluster boot, if that was really the concern,
> > all nodes would grab and activate the VG, as it is untagged...
>
> That's not how it works. You have to take ownership of the volume
> before you can activate it. Untagged does not mean a node can
> activate it without first explicitly setting the tag.
The scenario is this (please correct me):
There are a number of hosts that can see the PVs for this VG.
Some of them may *not* be part of the pacemaker cluster.
But *ALL* of them have their lvm.conf contain the equivalent of
global { locking_type = 1 }
tags { hosttags = 1 }
activation { volume_list = [ "@*" ] }
If any node is able to see the PVs, but has volume_list undefined,
"vgchange -ay" would activate it anyways.
So we are back at "Don't do that".
> I've tested this specific scenario and was unable to activate the
> volume group manually without grabbing the tag first. Have you tested
> this and found something contrary to my results? This is how the
> feature is supposed to work.
See above ;-) no hosttags =1, no volume_list, no checking against it.
Granted, the lvm.conf would be prepared at deployment time,
so let's assume it is setup ok on all hosts accross the site anyways.
Still, I don't see what we gain by
check tag against my name
if not me, check tag againts membership list
not present
strip all tags and add my name
try vgchange -ay
instead of doing just
strip all tags and add my name
try vgchange -ay
In what scenario (appart from Pacemaker not being able to count to 1)
would the more elaborate version protect us better than the simple one,
and against what?
--
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com
DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
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