HP Labs Technical Reports



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Modelling Disks

Ruemmler, Chris; Wilkes, John

HPL-93-68

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Abstract: As processor speeds continue to increase rapidly, I/O is in danger of becoming a performance bottleneck. As a result, many researchers have started to look at ways to improve overall I/O performance-a large component of which is the performance of the disk itself. Many of these studies use analytical or simulation models to compare alternative approaches, and the quality of these models determines the quality of the conclusions: the wrong simplifying assumptions can even lead to erroneous conclusions. Unfortunately, the level of quality of the models used in practice varies widely-at least in part because the data needed to build a good one has not been readily available This paper makes three main contributions: (1)it provides a description of the current state of the art in disk drive technology and the underlying technology trends, with particular emphasis on those features that are likely to be of value to researchers constructing simulations; (2)it shows how to construct an accurate disk simulation model; and (3)it provides quantitative information on how the different portions of the model contribute to its accuracy. The primary audience for the paper is researchers engaged in I/O system studies, for whom it provides a wealth of information to assist them in producing more accurate simulation models with which to test out their ideas. It should also be of interest to anybody who would like to understand modern disk drive technology, and trends in its evolution.

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