An IO Scheduling Algorithm to Improve Performance of Flash-Based Solid State Disks

Since the emergence of solid state devices into the storage scene, improvements in capacity and price have brought them to the point where they are becoming a viable alternative to traditional magnetic storage media. Current file systems and device-level I/O schedulers are optimized for rotational magnetic hard disk drives. In order to improve the efficiency of hard disk utilization, an Operating System (OS) reschedules IO requests to examine more read and write requests in one disk rotation. The pattern of the reordered IO requests is modified from its original sequential sequence to a random sequence. However, a random sequence of IO requests may impose large performance and endurance overhead to solid state devices. Since solid state devices have drastically different properties and structures than hard disks, we need to revisit some design aspects of file systems and scheduling algorithms used in the I/O subsystem. In this thesis, we first extract Linux IO access traces using the block I/O level of file system. Then, using the disk IO traces, we investigate the current approaches to I/O scheduling. Our results reveal that the current schedulers may not be ideally suited for solid-state devices. We also propose an SSD-aware scheduler, which can improve the performance of the disk subsystem. The proposed IO scheduler has been implemented in the Linux Kernel and has been evaluated using the DiskSim. The results prove that the throughput of the proposed idea has been improved 56, 59.6, 170.6 and 47.3 percent in comparison with Noop, Anticipatory, CFQ and Deadline schedulers respectively.