On 03/17/2016 05:10 PM, Christopher Harvey wrote: > If I ignore pacemaker's existence, and just run corosync, corosync > disagrees about node membership in the situation presented in the first > email. While it's true that stonith just happens to quickly correct the > situation after it occurs it still smells like a bug in the case where > corosync in used in isolation. Corosync is after all a membership and > total ordering protocol, and the nodes in the cluster are unable to > agree on membership. > > The Totem protocol specifies a ring_id in the token passed in a ring. > Since all of the 3 nodes but one have formed a new ring with a new id > how is it that the single node can survive in a ring with no other > members passing a token with the old ring_id? > > Are there network failure situations that can fool the Totem membership > protocol or is this an implementation problem? I don't see how it could > not be one or the other, and it's bad either way.
Neither, really. In a split brain situation, there simply is not enough information for any protocol or implementation to reliably decide what to do. That's what fencing is meant to solve -- it provides the information that certain nodes are definitely not active. There's no way for either side of the split to know whether the opposite side is down, or merely unable to communicate properly. If the latter, it's possible that they are still accessing shared resources, which without proper communication, can lead to serious problems (e.g. data corruption of a shared volume). _______________________________________________ Users mailing list: [email protected] http://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
