[Pacemaker] Strange behaviour of dual master DRBD

[Lars Ellenberg]

On Fri, Sep 11, 2009 at 09:50:56AM +0200, Michael Schwartzkopff wrote:
> Am Donnerstag, 10. September 2009 19:25:53 schrieb Lars Ellenberg:
> > On Thu, Sep 10, 2009 at 05:10:39PM +0200, Michael Schwartzkopff wrote:
> > > Hi,
> > >
> > > I configured a dual master DRBD-8.3.2. When the nodes stat there is no
> > > problem. Both DRBD become master. But when I set on node to standby and
> > > wake it up again, the DRBD on that node stays secondary and does not
> > > become master.
> > >
> > > My config:
> > > primitive resDRBD ocf:linbit:drbd params drbd_resource="r0"
> > > ms msDRBD resDRBD meta notify="true" master-max="2"
> > >
> > > No further constraints.
> > >
> > > When the second node is online again ptest -sL shows:
> > > (...)
> > > resDRBD:0 promotion score on suse2: 50
> > > resDRBD:1 promotion scpre on suse1: -1
> > >
> > > Since the "-1" prevents the resource from beein promoted, I understand
> > > the behaviour of the cluster, but why isn't the resource beeing allowed
> > > th become master on that node?
> > >
> > > Thanks for any enlightenting answers.
> >
> > Most likely it prevents you from shoting yourself in the foot ;)
> >
> > look at /proc/drbd and the kernel logs (appart from the ha.log, of
> > course) on the drbd nodes to find out more.
> > I bet you manoevered yourself into diverging data sets (aka DRBD "split
> > brain").
> >
> > If it turns out to be a drbd.ocf bug,
> > let me know.
> 
> Hi,
> 
> another confusing fact:
> 
> The primitive DRBD was created without a monitor operation. When I add a 
> monitor operation, better two (Master,Slave) the described problem goes away. 
> But in my understanding the complete setup should work as expected WITHOUT the 
> monitoring operation.

Well, your understanding is wrong.
If you want the details,
there is a lot of magic going on associated with the master scores,
see the drbd.ocf script, drbd_update_master_score.

You should definitely configure notify.
You may get away without notify, if you configure monitor,
and wait for a few monitor actions to happen.


-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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