Hi! With an sbd running on each node, I think it doesn't make a big differentce wich one was started first in cas eof a split brain: There is a chance that both nodes will kill each other.
I'd put my efforts into redundant reliable networking instead (MHO)... Regards, Ulrich > Wrapping my head around how pcmk_delay_max works, my understanding is > > - on startup pacemaker always starts one instance of stonith/sbd; it > probably randomly selects node for it. I suppose this initial start is > delayed by random number within pcmk_delay_max. > > - when cluster is partitioned, pacemaker *also* starts one instance of > stonith/sbd in each partition where it is not yet running. This startup > is also delayed by random number within pcmk_delay_max. > > - this makes partition that already has stonith/sbd running win race for > kill request > > Is my understanding correct? > > If yes, consider two node cluster where one application is more > important than the other. The obvious example is replicated database - > in case of split brain we want to preserve node with primary as it > likely has active connections. > > Would using advisory colocation constraint between application and > stonith/sbd work? Let's consider (using crmsh notation) > > primitive my_database > ms my_replicated_database my_database > primitive fencing_sbd stonith:external/sbd params pcmk_delay_max=15 > colocation prefer_primary 10: fencing_sbd my_replicated_database:Master > > It is going to work? > > It should work on startup, as it simply affects where sbd resource is > placed initially and pacemaker need to make this decision anyway. > > I expect it to work if my_primary_database master moves to another node > - pacemaker should move sbd resource too, right? It does add small > window where no stonith agent is running, but as I understand pacemaker > is going to start it anyway in case of split brain, so in the worst case > non-preferred node will be fenced, which is not worse than what we have > already. > > What I am not sure is what happens during split brain. Will colocation > affect pacemaker decision to start another copy of sbd resource on > another partitioned node? I hope not, as it is advisory so it should > still use the only available node left in this case? > > Does it all make sense? Anyone has used it in real life? > > > _______________________________________________ > Users mailing list: Users@clusterlabs.org > http://lists.clusterlabs.org/mailman/listinfo/users > > Project Home: http://www.clusterlabs.org > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf > Bugs: http://bugs.clusterlabs.org _______________________________________________ Users mailing list: Users@clusterlabs.org http://lists.clusterlabs.org/mailman/listinfo/users Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org