They do talk about this:<p>&gt; <i>When the system was built, one of the missing features from Kafka 0.7 was the ability of the Kafka Broker cluster to behave as a reliable persistent storage. This influenced a major design decision to not keep persistent state between the producer of data, Kafka Syslog Producer, and Hadoop. An event is considered reliably persisted only when it gets written to a file on HDFS.</i>