[Pacemaker] problem with colocating and ordering sets of resources

[Ronney Meier - Rorotec Informatik GmbH]

> > Hi all
> >
> > I have a 2 node setup with lvm on top oft wo drbd devices and two xen
> virtual machines running.
> > The pacemaker version used is 1.0.11 .
> > All of the resources should always be running on the same node.
> > This usually works, but last week after a crash it happened, that pacemaker
> made one of the drbd devices master on one node, and the other drbd
> device on the other node. So it couldn't bring up the lvm anymore and
> therefore also none of the other resources were able to run.
> > My colocation and order constraints look like that here:
> >
> > colocation xen_on_drbd inf: ( xen-windows_server_sb
> > xen-windows_server_standard ) fs-xendata lv-drbd_data (
> > ms-drbd_r0:Master ms-drbd_r1:Master )
> >
> > order ord-xen_after_drbd inf: ( ms-drbd_r0:promote ms-drbd_r1:promote
> > ) lv-drbd_data:start fs-xendata:start ( xen-windows_server_sb:start
> > xen-windows_server_standard:start )
> >
> > So that it should first promote the two drbd devices, then den bringing up
> the lvm (=lv-drbd_data), then mounting the filesystem with the xen images
> (=fs_xendata) and then starting up the virtual machines.
> > Resources in the colocation constraint inside of parenthesis should be
> independent from each other.
> >
> > If I didn't completely missunderstood how the colocation of sets works, it
> should be impossible, that pacemaker promotes the two drbd devices on
> different nodes.
> > Or did I make an error with these constraints?
> 
> Yes, you make an error ;-) ... if you set the parenthesis around resources you
> set the sequential attribute to false. For an order resource sets that means:
> unordered. For a colocation set it means: not colocated ... and that is what
> you saw in you setup.
> 
> 
> Remove the parenthesis around the DRBD masters in your colocation and
> everything should be fine.
> 
> Are these two DRBD devices acting as two PVs for one VG? This is not a
> recommended setup because ... as you already saw ... the two DRBD master
> could end on different nodes or be disconnected individually having a
> different data generation in case of an failover and then you have serious
> problems with your VG. This can be handled properly in DRBD 8.4.x. that
> supports serveral volumes per connection.
> 
> Regards,
> Andreas

Hi andreas

Thanks a lot for your answer.

I was aware about what the sequential attribute means for an order resource...