Real-Time Disk Scheduling with On-Disk Cache Conscious

Previous real-time disk scheduling algorithms assume that each disk request incurs a disk mechanical operation and only consider how to move the disk head under real-time constraints. However, with the increased capacity of on-disk cache, modern disk drives read-ahead data aggressively. Thus, the ondisk cache may service lots of requests without incurring physical disk access. By exploring the design methodology of on-disk cache, in this paper, we propose CARDS: a cache-aware real-time disk scheduling algorithm that takes the on-disk cache into consideration during scheduling. Therefore, the scheduling algorithm can help to minimize the cache miss ratio. Besides, the service timing estimation is more accurate in schedulability analysis since the cache effect is considered. A simulation-based evaluation shows CARDS to be highly successful as compared to the classical real-time disk scheduling algorithms. For example, under sequential workload with 10 sequential streams, the data throughput of CARDS is 1.1 times of DM-SCAN.