----- Original Message -----
> From: "David Vossel" <[email protected]>
> To: "General Linux-HA mailing list" <[email protected]>
> Sent: Monday, June 3, 2013 10:50:01 AM
> Subject: Re: [Linux-HA] LVM Resource agent, "exclusive" activation
>
> ----- Original Message -----
> > From: "Lars Ellenberg" <[email protected]>
> > To: [email protected]
> > Sent: Tuesday, May 21, 2013 5:58:05 PM
> > Subject: Re: [Linux-HA] LVM Resource agent, "exclusive" activation
> >
> > On Tue, May 21, 2013 at 05:52:39PM -0400, David Vossel wrote:
> > > ----- Original Message -----
> > > > From: "Lars Ellenberg" <[email protected]>
> > > > To: "Brassow Jonathan" <[email protected]>
> > > > Cc: "General Linux-HA mailing list" <[email protected]>,
> > > > "Lars
> > > > Marowsky-Bree" <[email protected]>, "Fabio M. Di
> > > > Nitto" <[email protected]>
> > > > Sent: Monday, May 20, 2013 3:50:49 PM
> > > > Subject: Re: [Linux-HA] LVM Resource agent, "exclusive" activation
> > > >
> > > > On Fri, May 17, 2013 at 02:00:48PM -0500, Brassow Jonathan wrote:
> > > > >
> > > > > On May 17, 2013, at 10:14 AM, Lars Ellenberg wrote:
> > > > >
> > > > > > On Thu, May 16, 2013 at 10:42:30AM -0400, David Vossel wrote:
> > > > > >
> > > > > >>>>>>> The use of 'auto_activation_volume_list' depends on updates
> > > > > >>>>>>> to
> > > > > >>>>>>> the
> > > > > >>>>>>> LVM
> > > > > >>>>>>> initscripts - ensuring that they use '-aay' in order to
> > > > > >>>>>>> activate
> > > > > >>>>>>> logical
> > > > > >>>>>>> volumes. That has been checked in upstream. I'm sure it
> > > > > >>>>>>> will
> > > > > >>>>>>> go
> > > > > >>>>>>> into
> > > > > >>>>>>> RHEL7 and I think (but would need to check on) RHEL6.
> > > > > >
> > > > > > Only that this is upstream here, so it better work with
> > > > > > debian oldstale, gentoo or archlinux as well ;-)
> > > > > >
> > > > > >
> > > > > > Would this be good enough:
> > > > > >
> > > > > > vgchange --addtag pacemaker $VG
> > > > > > and NOT mention the "pacemaker" tag anywhere in lvm.conf ...
> > > > > > then, in the agent start action,
> > > > > > vgchange -ay --config "tags { pacemaker {} }" $VG
> > > > > >
> > > > > > (or have the to be used tag as an additional parameter)
> > > > > >
> > > > > > No retagging necessary.
> > > > > >
> > > > > > How far back do the lvm tools understand the "--config ..." option?
> > > > >
> > > > > --config option goes back years and years - not sure of the exact
> > > > > date,
> > > > > but
> > > > > could probably tell with 'git bisect' if you wanted me to.
> > > > >
> > > > > The above would not quite be sufficient.
> > > > > You would still have to change the 'volume_list' field in lvm.conf
> > > > > (and
> > > > > update the initrd).
> > > >
> > > > You have to do that anyways if you want to make use of tags in this
> > > > way?
> > > >
> > > > > What you are proposing would simplify things in that you would not
> > > > > need different 'volume_list's on each machine - you could copy
> > > > > configs
> > > > > between machines.
> > > >
> > > > I thought volume_list = [ ... , "@*" ] in lvm.conf,
> > > > assuming that works on all "relevant" distributions as well,
> > > > and a command line "--config" tag would also propagate into that @*.
> > > > It did so for me.
> > > >
> > > > But yes, vlumen_list = [ ... , "pacemaker" ] would be fine as well.
> > >
> > > wait, did we just go around in a circle. If we add "pacemaker" to the
> > > volume list, and use that in every cluster node's config, then we've
> > > by-passed the exclusive activation part have we not?!
> >
> > No. I suggested to NOT set that "pacemaker" tag in the config (lvm.conf),
> > but only ever explicitly set that tag from the command line as used from
> > the resource agent ( --config "tags { pacemaker {} }" )
> >
> > That would also mean to either override volume_list with the same
> > command line, or to have the tag mentioned in the volume_list in
> > lvm.conf (but not set it in the tags {} section).
> >
> > > Also, we're not happy with the auto_activate list because it won't
> > > work with old distros?! It's a new feature, why do we have to work
> > > with old distros that don't support it?
> >
> > You are right, we only have to make sure we don't break existing setup
> > by rolling out a new version of the RA. So if the resource agent
> > won't "accidentally" use a code path where support of a new feature
> > (of LVM) would be required, that's "good enough" compatibility.
> >
> > Still it won't hurt to pick the most "compatible" implementation
> > of several possible "equivalent" ones (RA-feature wise).
> >
> > I think the proposed --config "tags { pacemaker {} }"
> > is simpler (no retagging, no re-writing of lvm meta data),
> > and will work for any setup that knows about tags.
>
> I've had a good talk with Jonathan about the --config "tags { pacemaker {} }"
> approach. This was originally complicated for us because we were using the
> --config option for a device filter during activation in certain
> situations... using the --config option twice caused problems which made
> adding the tag in the config difficult.
>
> We've worked through those situations and it looks like it is actually safe
> to strip out the conflicting --config usage required for the resilient
> device filtering on activation.
>
> The path forward is this.
>
> 1. Now that I know certain things are safe to remove, I'm going to
> re-evaluate my current patches and attempt to greatly simplify the number of
> changes to the original LVM agent. All the looking at the cluster
> membership and resilient activation checking can be thrown out.
>
> 2. Next I'm going to introduce the proposed --config tags feature as a
> separate patch that enables exclusive activation functionality without
> clvmd.
The plan to set 'volume_list=["@*"]' in lvm.conf and override the tags during
the activation using "vgchange -ay --config 'tags{ mytag{} }' vg0" does not
work.
As a similar alternative, I am forcing the volume_list in lvm.conf to be
initialized and not contain the tag the cluster is using for exclusive
activation, and then overriding the volume_list during the activation to allow
volume groups with the cluster tag to be activated. This is a very similar
approach to what Lars original proposed.
I have finished my initial work on the new set of patches. They can be found in
this pull request. https://github.com/ClusterLabs/resource-agents/pull/252
This new direction is much less invasive than the previous set of patches.
-- Vossel
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