[Pacemaker] A/P Corosync, PGSQL and Split Brains questions

[Stephan-Frank Henry]

> On: Thu, 10 Feb 2011 08:51:01 +0100, Andrew Beekhof wrote:
> On Wed, Feb 9, 2011 at 2:48 PM, Stephan-Frank Henry <Frank.Henry at gmx.net>
> wrote:
> > Hello agian,
> >
> > after fixing up my VirtualIP problem, I have been doing some Split Brain
> tests and while everything 'returns to normal', it is not quite what I had
> desired.
> >
> > My scenario:
> > Acive/Passive 2 node cluster (serverA & serverB) with Corosync, DRBD &
> PGSQL.
> > The resources are configured as Master/Slave and sofar it is fine.
> >
> > Since bullet points speak more then words: ;)
> > Test:
> >  1) Pull the plug on the master (serverA)
> >  2) Then Reattach
> 
> You forgot
> 0) Configure stonith
> 
> If data is being written to both sides, one of the sets is always
> going to be lost.

Agreed and acceptable, it is more a question of who survives.
And that is maybe where my confusion lies, I always thought stonith would actually shut down the 'zombie' node (as STONITH would imply).
Thus I would lose the zombie node.

I would like that when the split brain is detected (not only on drbd) the one that has the latest data will retain the master roll, and the slave syncs up.
Am I asking the impossible?

If this is not possible, also no problem! I am just seeking clarification.

I'll check out the black magic called STONITH now. :D

> > Expected results:
> >  1) serverB becomes Master
> 
> You mean master for the drbd resource right?
> Actually I'd expect both sides would be promoted - there is no way for
> either server to know whether it or its peer is dead.

Yes, naturally (sorry). Both become master (from the outside it is only the one that remains) and that all works fine.

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