Yitzhak Dishon

Design innovations of the IBM 3830 and 2835 storage control units

The IBM 2305 Fixed Head Storage and IBM 3330 Disk Storage provide significant performance improvements over previously available disk facilities. Many of the improvements were made possible by the design of the control units, which are complex systems that integrate analog and digital interfaces. Definition of control unit requirements and characteristics permitted a large degree of commonality to be achieved between the two control units. The available design alternatives and implementations are discussed.

Disk dual copy methods and their performance

Performance analyses of three dual-copy methods for ensuring fault tolerance of disk storage devices are considered: an algorithm using synchronized disks, and single-read and parallel-read algorithms using nonsynchronized disks. With the synchronized algorithm, dual copying of data is performed almost simultaneously for every write request. With nonsynchronized disks, the two write operations are essentially sequential. Thus the coordination of the two physical data transfers for each write request degrades performance. On the other hand, the availability of dual copies of the data makes it possible to save on rotational latency time by connecting to that device whose rotational position is closest to the read/write head, thus improving performance.<<ETX>>