Overlapped disk access for real-time disk I/O

Disk subsystems of soft real time systems are designed to meet the deadlines of the real time disk I/O commands as much as possible. The paper examines methods to get the best out of active hardware components in a disk drive and evaluates the real time performances of the methods. Some of the active hardware components in a disk drive are idle for some time, while a disk I/O command is being serviced by some active hardware components in the disk drive. If the idle time is used for the next pending disk I/O command, the disk I/O command could be serviced much earlier. We develop three models of overlapped disk access which service two adjacent disk I/O commands concurrently by overlapping. The new disk model embedding the overlapped disk access methods is also proposed. It is evaluated via simulations, and its real time performance is compared with traditional disk drives. The results of the performance evaluation show that the proposed disk model has a much better real time performance than traditional disk drives in real time computing environments