Scheduling algorithms for modern disk drives

  • Authors:

  • Bruce L. Worthington;Gregory R. Ganger;Yale N. Patt

  • Affiliations:

  • Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor;Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor;Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

  • Venue:
  • SIGMETRICS '94 Proceedings of the 1994 ACM SIGMETRICS conference on Measurement and modeling of computer systems
  • Year:
  • 1994

Quantified Score

Hi-index 0.02

Visualization

Abstract

Disk subsystem performance can be dramatically improved by dynamically ordering, or scheduling, pending requests. Via strongly validated simulation, we examine the impact of complex logical-to-physical mappings and large prefetching caches on scheduling effectiveness. Using both synthetic workloads and traces captured from six different user environments, we arrive at three main conclusions: (1) Incorporating complex mapping information into the scheduler provides only a marginal (less than 2%) decrease in response times for seek-reducing algorithms. (2) Algorithms which effectively utilize prefetching disk caches provide significant performance improvements for workloads with read sequentiality. The cyclical scan algorithm (C-LOOK), which always schedules requests in ascending logical order, achieves the highest performance among seek-reducing algorithms for such workloads. (3) Algorithms that reduce overall positioning delays produce the highest performance provided that they recognize and exploit a prefetching cache.