Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Metadata controller (or MDC) is a storage area network (SAN) technology for managing file locking, space allocation and data access authorization. This is needed when several clients are given block level access to the same disk volume. A storage area network (SAN) is a storage device (such as disk arrays, tape libraries, and optical jukeboxes) to servers so the devices appear as locally attached to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the regular network by regular devices. The cost and complexity of SANs dropped in the late 2000s, allowing wider adoption across both enterprise and small to medium sized business environments.