From the category “if you didn’t read the paper1, here is a good summary of it”, Todd Hoff’s notes about Riak’s Bitcask.
Eric Brewer (CAP theorem) came up with idea with Bitcask by considering if you have the capacity to keep all keys in memory, which is quite likely on modern systems, you can have a relatively easy to design and implement storage system. The commit log can be used as the database itself, providing atomicity and durability. Only one write is required to persist the data. Separate writes to a data file and a commit log is not necessary.
Since Riak 0.11.0, Bitcask is the default storage engine.
Original title and link: Riak Bitcask Explained (NoSQL databases © myNoSQL)