Replication factor (RF) controls how many copies of each partition exist across brokers. RF=3 means every message is stored on 3 brokers. The In-Sync Replica set (ISR) tracks which replicas are fully caught up. min.insync.replicas (minISR) is the minimum ISR size the leader requires before acknowledging a write — protecting against silent data loss.
Key configuration
replication.factor=3 (topic level)
min.insync.replicas=2 (topic level)
default.replication.factor=3 (broker level)