Rotational-Position-Aware Real-Time Disk SchedulingUsing a Dynamic Active Subset (DAS)

Abstract Scheduling disk requests with service guarantees hasto bring the demand to meet guarantees in line with the need to optimize disk utilization. This paper presents thedesign, implementation and experimental evaluation of a disk-scheduling framework which optimizes the disk utiliza-tion under the constraints of both hard and statistical service guarantees. The framework is based on two princi-ples: 1) upon each scheduling decision, the calculation of a subset of the outstanding disk requests such that all ser-vice guarantees can be enforced under worst-case assumptions and 2) the scheduling of this subset based on the ro-tational position of requests in order to improve the disk utilization. Results are presented through an implementa-tion of the scheduling framework in DROPS, the Dresden Real-Time Operating System