Flexible Paxos provides us the insight that Paxos (and Raft) only need that election and replication quorums intersect. But standard Raft and Paxos are configured so that every quorum intersects. So what does that mean exactly?

Let’s take the election quorum and Raft. An election quorum is a subset of the set of servers that have voted for the same server in the same election term and that quorum is formed of a majority. For a 3 node cluster we need 2 votes and a 5 node cluster we need 3 votes and so on.

The next question is: what are all the possible quorums that exist and are there any two quorums that do not intersect? The possible majority quorums are {n1, n2}, {n2, n3} and {n1, n3} and there are no two quorums that do not intersect. This is the property we get from majority quorums.