In today\u27s computer systems, the disk I/O subsystem is often identified as a major bottleneck to system performance. Removing this bottleneck has proven to be a challenging research problem. The research reported in this dissertation is motivated by the design and performance issues of disk I/O subsystems for a variety of today\u27s computing systems. The goal is to design and evaluate high performance I/O subsystems for computing systems which support various applications. Our contributions are three-fold: for different application areas, we (1) propose new architecture and scheduling policies for the disk I/O subsystems; (2) develop analytic models and simulators for these disk subsystems; and (3) study and compare the performance of these architectures and scheduling policies. First, we study a mirrored disk which can be found in various fault tolerant systems, where each data item is duplicated. While the primary purpose of disk mirroring is to provide the fault tolerance, we are interested in how to achieve performance gain by taking advantage of the two data copies. In particular, we propose and examine several policies which differ according to the manner in which read requests are scheduled to one of the two copies. Analytic models are developed to model the behavior of these policies and the best policies are proposed. In addition, the modeling techniques developed in this study are of independent interest, which can be used or extended to other system studies. Second, we investigate existing and propose new disk array architectures for high performance computing systems. Depending on the applications, we propose scheduling policies suitable for these architectures. In particular, we study three variations of RAID 1, mirrored declustering, chained declustering, and group-rotate declustering. We compare the performance of RAID 5 versus Parity Striping. Finally, we examine the performance/cost trade-off of RAID 1 and RAID 5. The performance studies of the various disk array architectures coupled with the proposed scheduling policies are based on our analytic models and simulators. Third, we examine the disk I/O subsystems for real-time systems, where each I/O is expected to complete before a deadline. The goal is to minimize the fraction of requests that miss their deadlines. In doing so, we first propose two new real-time disk scheduling algorithms, and compare them with other known real-time or conventional algorithms in an integrated real-time transaction system model. We then extend this study to a mirrored disk and disk arrays by combining the real-time algorithms with the architectures and policies studied before. Last, we study disk I/O in a non-removal real-time system environment
