[Pacemaker] Mail notification for fencing action

[Dejan Muhamedagic]

On Wed, Jun 15, 2011 at 03:26:56PM -0500, mark - pacemaker list wrote:
> On Wed, Jun 15, 2011 at 12:24 PM, imnotpc <imnotpc at rock3d.net> wrote:
> 
> >
> > What I was thinking is that the DC is never fenced
> 
> 
> Is this actually the case?

In a way it is true. Only DC can order fencing and there is
always exactly one DC in a partition. On split brain, each
partition elects a DC and if the DC has quorum it can try to
fence nodes in other partitions. That's why in two-node clusters
there's always a shoot-out. But note that the old DC (before
split brain), if it loses quorum, gets fenced by a new DC from
another partition.

> It would sure explain the one "gotcha" I've
> never been able to work around in a three node cluster with stonith/SBD.  If
> you unplug the network cable from the DC (but it and the other nodes all
> still see the SBD disk via their other NIC(s)), the DC of course becomes
> completely isolated.  It will fence

Fence? It won't fence anything unless it has quorum. Do you have
no-quorum-policy=ignore?

Thanks,

Dejan

> one of the still good nodes right away,
> and the surviving node that still has network connectivity will become DC.
>  So, you have two DCs, the original one which is disconnected from the
> network and your newly elected one (not really elected, just took over
> because it's the last host left that has network).  When the just-fenced
> node comes back up, you get quorum with the new DC and your disconnected DC
> finally gets shot.
> 
> For any non-DC node, you get exactly the behavior you'd expect, where
> unplugging its network cable gets it fenced and everyone else stays happy.
>  I'd hoped for a situation where unplugging the DC would have the other two
> say, "well, our DC is gone, but we can see each other so he need to be
> fenced".  Maybe I've just missed a necessary timeout setting somewhere to
> delay the isolated DC from fencing a good node so quickly?
> 
> Sorry, I guess that's a thread hijack, but I've looked and googled and never
> anywhere been able to find something that says DCs don't get fenced, so this
> has confused me for a bit.
> 
> Regards,
> Mark

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