Anticipatory disk arm placement to reduce seek time

Document Type

Article

Publication Date

5-1-2006

Abstract

We investigate anticipatory arm placement (AAP) to minimize the disk seek distance and its time. Reducing disk access time via AAP is the best that can be done since latency cannot be improved. We consider uniform and hot-spot disk access models on single and multiple disks without and with zoning.The uniform model results in uniform accesses to the C disk cylinders in non-zoned disks and accesses with a frequency proportional to the number of blocks on a cylinder in zoned disks.The hot-spot model accesses a hot-spot cylinder with probability p, while other cylinders are accessed uniformly with probability (1 - p)/C ≪K C. We express the seek distances with continuous functions and obtain the optimal point for AAP by minimizing them in each case. Well known results in AAP, e.g., the two arms in mirrored disks should be placed at one quarter of the maximum seek distance from outer and inner disk cylinders, are verified and other new interesting results are derived. Simulation results show that with increasing disk utilization AAP results in a degradation in response time as compared with no AAP and that AAP works better with mirrored disks. © 2006 CRL Publishing Ltd.

Identifier

33746210265 (Scopus)

Publication Title

Computer Systems Science and Engineering

ISSN

02676192

First Page

173

Last Page

182

Issue

3

Volume

21

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