Disk management for a hard real-time file system

Abstract

The problem of scheduling disk requests in a personal hard real-time read/write file system is examined. 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 an the file system parameters. A configuration program is developed to automatically test and configure the FSCAN algorithm for modern hard disks. The design and testing of this program are described.