The number of replicas for a topic can be tweaked with the setting replication.factor. For topics created automatically, the setting is default.replication.factor. If the replication factor is set to three, then each partition of a topic gets replicated to three different brokers. In general, if the replication factor is F we can afford to lose F-1 brokers without affecting reliability. However, in older Kafka versions when F is set to 2, unavailability might still be experienced when one of the brokers goes down, thus sending the cluster in an unstable state. A higher replication factor leads to higher availability, higher reliability, and fewer disasters. You may come across a replication factor set to 5 for highly critical topics in the industry. Kafka also has the intelligence to place the replica in different racks to protect against rack failures. The rack a broker lives in can be provided to Kafka using the broker configuration parameter broker.rack.