A structured approach to redundant disk array implementation

Abstract

Error recovery in redundant disk arrays is typically performed in an ad hoc fashion, requiring architecture-specific code which limits extensibility and is difficult to verify. In this paper, we describe a technique for automating the execution of redundant disk array operations, including recovery from errors, independent of array architecture. Our approach employs a graphical representation of array operations and a two-phase error recovery scheme we refer to as roll-away error recovery. We demonstrate the validity of this approach in RAID-frame, a prototyping framework that separates architectural policy from execution mechanism. RAID-frame facilitates rapid prototyping of new RAID architectures by localizing modifications. In addition, RAID-frame implemented architectures run the same code when configured as an event-driven simulator, a user-level application managing raw disks, and as a Digital Unix device-driver capable of mounting a filesystem. Evaluation shows that RAID-frame performance is equivalent to less complex array implementations and that case studies of RAID levels 0, 1, 4, 5, 6, and parity declustering achieve expected performance.