DiskModelling-Ruemner

DiskModelling-Ruemner - An introduction to disk drive...

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Unformatted text preview: An introduction to disk drive modeling Chris Ruemmler and John Wilkes Hewlett-Packard Laboratories, Palo Alto, CA Much research in I/O systems is based on disk drive simulation models, but how good are they? An accurate simulation model should emphasize the performance- critical areas. This paper has been published in IEEE Computer 27 (3):1729, March 1994. It supersedes HP Labs technical reports HPL9368 rev 1 and HPLOSR9329. Copyright 1994 IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE. To receive more information on obtaining permission, send a blank email message to info.pub.permission@ieee.org. Note : this file was obtained by scanning and performing OCR on the IEEE published copy. As a result, it may contain typographic or other errors that are not in the published version. Minor clarifications and updates have been made to the bibliography. 1 Modern microprocessor technology is advancing at an incredible rate, and speedups of 40 to 60 percent compounded annually have become the norm. Although disk storage densities are also improving impressively (60 to 80 percent compounded annually), performance improvements have been occurring at only about 7 to 10 percent compounded annually over the last decade. As a result, disk system performance is fast becoming a dominant factor in overall system behavior. Naturally, researchers want to improve overall I/O performance, of which a large component is the performance of the disk drive itself. This research often involves using analytical or simulation models to compare alternative approaches, and the quality of these models determines the quality of the conclusions; indeed, the wrong modeling assumptions can lead to erroneous conclusions. Nevertheless, little work has been done to develop or describe accurate disk drive models. This may explain the commonplace use of simple, relatively inaccurate models. We believe there is much room for improvement. This article demonstrates and describes a calibrated, high- quality disk drive model in which the overall error factor is 14 times smaller than that of a simple first-order model. We describe the various disk drive performance components separately, then show how their inclusion improves the simulation model. This enables an informed trade-off between effort and accuracy. In addition, we provide detailed characteristics for two disk drives, as well as a brief description of a simulation environment that uses the disk drive model. Characteristics of modern disk drives To model disk drives, we must understand how they behave. Thus, we begin with an overview of the current state of the art in nonremovable magnetic disk drives with embedded SCSI (Small Computer Systems Interconnect) controllers, since these are widely available....
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DiskModelling-Ruemner - An introduction to disk drive...

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