Up to this point, we have considered a few essential concepts in clustering, leading to the following not completely fictitious scenario—what happens if a cluster is formed by nodes that are located in separate networks and the communication link between them goes down? The same applies when the nodes are in the same network and the link goes down as well. That is, none of the nodes have actually gone offline, but each appears to the other as unavailable. The default behavior would be that each node assumes that the other is down and continues serving whatever resources or applications the cluster was previously running.
So far, so good! Now, let's say the network link comes back online but both nodes still think they are the main cluster member. That is where data corruption—at the worst—or inconsistency—at the best—occur. This is caused by possible changes made to data on either side without having been replicated to the other end.
This is...