The storage server as virtual volume manager

The storage server function has undergone considerable change since Version 4 of the Mass Storage System Reference Model. The authors survey the major changes in the storage server, and motivate a number of storage server concepts and functions through a survey of commercial storage volume management products. A classification of physical storage devices by their major attributes is presented as a physical volume model. The virtual volume model is presented as a recursive composition of physical extents of physical volumes. Finally, the authors propose a restructuring of the service primitives between model layers to simplify interfaces and support arbitrary device-to-device transfers without intermediate copies