Operating system support for the management of hard real-time disk traffic

Emerging applications like C3I systems, real-time databases, data acquisition systems and multimedia servers require access to secondary storage devices under timing constraints. In this paper, we focus on operating system support needed for managing real-time disk traffic with hard deadlines. We present the design and implementation of a preemptive deadline-driven disk I/O subsystem suitable for real-time disk traffic management. Preemptibility is achieved with a granularity that is automatically controlled by the I/O subsystem according to current workload and filesystem data layout. An admission control test checks the current resource availability for a given workload. We show that contiguous layout is necessary to maintain hard real-time guarantees and a reasonable level of disk throughput. Finally, we show how buffering can be used to obtain utilization factors close to the maximum disk bandwidth possible.