Scheduling Multiple Flows on Parallel Disk Systems

Abstract. We examine the problem of scheduling concurrent independent flows on multiple-disk I/O storage systems. Two models are considered: in the shared buffer model the memory buffer is shared among all the disks, while in the partitioned buffer model each flow has a private buffer. For the parallel disk model with d> 1 disks it is shown that the problem of minimizing the schedule length of n> 2 concurrent flows is NP-complete for both buffer models. A randomized scheduling algorithm for the partitioned buffer model is analyzed and probabilistic bounds on the schedule length are presented. Finally a heuristic based on static buffer allocation for the shared buffer model is discussed.

Parallel Prefetching and Caching Is Hard

In this paper we study integrated prefetching and caching in parallel disk systems. This topic has gained a lot of interest in the last years which manifests itself in numerous recent approximation algorithms. This paper provides the first negative result in this area by showing that optimizing the stall time is APX-hard. This also implies that computing the optimal processing time is NP-hard, which settles an open problem posed by Kimbrel and Karlin