You must assign at least one computer to become a controller when setting up your SAN. This machine has the job of maintaining the volume metadata of the SAN, file journaling, and concurrent access to files. This controller "remembers" which RAIDs are part of a pool, and how you have configured your pools to make volumes. Although the controller is in charge of these tasks, the actual data is stored on the SAN. In the event of failure of the main controller, Xsan will automatically switch to the backup controller. The backup controller is aware of how the SAN is configured, so if failure occurs, and the backup kicks into action, clients are often unaware that anything has happened. |