> http://wiki.apache.org/cassandra/ArchitectureSSTable
Be aware that this page hasn't been updated since 2013, so it doesn't reflect any changes to the SSTable format since then, including the new storage engine introduced in 3.0 (see CASSANDRA-8099). That said, I believe the linked Apache wiki page is the best documentation for the format. Unfortunately, if you want a better or more current understanding, you'll have to read the code and read some SSTables.
