Disk management for a hard real-time file system

The problem of scheduling disk requests in a personal hard real-time read/write file system is examined. It is shown that any optimal algorithm for a simplified disk scheduling can be forced to thrash very badly. To avoid thrashing, we propose a fixed-period scan (FSCAN), approach for disk scheduling in our file system. The idea is to use the CSCAN policy to pick up the data blocks requested by a periodic preemptive schedule. The approach trades disk block size and memory buffer size for higher performance. We derive the worst case seek and rotational overhead for the FSCAN algorithm, and we show that the worst-case seek overhead can be measured empirically for a large class of seek functions. Using this approach and utilizing measured seek functions from real disk drives, we show that these policies can transfer data at 40-70% of the maximum transfer rate of modern disk drives, depending on the file system parameters. A configuration program is developed to automatically test and configure the FSCAN algorithm for modern hard disks. The design, implementation and testing of this program are described.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat