Runtime behavior on one node — why a cold engine takes minutes to become a serving machine, which knobs are operational and which are redeployments, choosing a degradation ladder before the machine chooses one for you, and why heterogeneous tenants are an asset.
Why w + r > n is a probability dial rather than a guarantee — the edge cases that return stale data anyway, the consistency guarantees quorums never provide, and why staleness is so hard to monitor.
What a leaderless database does when a client cannot reach its quorum at all — why the fix buys durability rather than consistency, and how the same model stretches across datacenters.
The operational side of leader-based replication — how to add a new follower without downtime, and what actually happens when nodes fail.