[Pacemaker] problem with colocating and ordering sets of resources

Andreas Kurz andreas at hastexo.com
Mon Nov 21 14:34:46 EST 2011

On 11/21/2011 07:40 PM, Ronney Meier - Rorotec Informatik GmbH wrote:
> 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.


Need help with Pacemaker?

> Thanks for any help in advance :-)
> ronney
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