"Introduction to MySQL Cluster The NDB storage engine (MySQL Cluster) is a high-availability storage engine for MySQL. It provides synchronous replication between storage nodes and many mysql servers having a consistent view of the database. In 4.1 and 5.0 it's a main memory database, but in 5.1 non-indexed attributes can be stored on disk. NDB also provides a lot of determinism in system resource usage. I'll talk a bit about that."