They are really in mebibytes (MiB). In the upcoming release of Cassandra, the configuration is getting standardised to KiB, MiB, etc, to remove ambiguity (CASSANDRA-15234 [1]). For more info, see Ekaterina Dimitrova's blog post [2]. Cheers!
[1] https://issues.apache.org/jira/browse/CASSANDRA-15234 [2] https://cassandra.apache.org/_/blog/Apache-Cassandra-4.1-Configuration-Standardization.html >
