Appeared in the Proc. Third NASA Goddard Conference on Mass Storage Systems and Technologies Oct. 1993.


Storage Media Pipelining: Making Good Use of Fine-Grained Media

Rodney Van Meter

Abstract:

This paper proposes a new high-performance paradigm for accessing removable media such as tapes and especially magneto-optical disks. In high-performance computing, striping of data across multiple devices is a common means of improving transfer rates. Striping has been used very successfully for fixed magnetic disks, improving overall system reliability as well as throughput. It has also been proposed as a solution for providing improved bandwidth for tape and magneto-optical subsystems. However, striping of removable media has shortcomings, partciularly in the areas of latency to data and restricted system configurations, and is suitable primarily for very large I/Os. We propose that for fine-grained media, an alternative access method, media pipelining, may be used to provide high bandwidth for large requests while retaining the flexibility to support concurrent small requests and different system configurations. Its principal drawback is high buffering requirements in the host computer or file server.

This paper discusses the possible organization of such a system, including the hardware conditions under which it may be effectibe, and the flexibility of configuration. Its expected performance is discussed under varying workloads, including large single I/Os and numerous smaller ones. Finally, a specific system incorporating a high-transfer-rate magneto-optical disk drive and autochanger is discussed.


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Rodney D. Van Meter III
Friday August 23, 1996