DiskSim is an efficient, accurate and highly-configurable disk system simulator developed at the University of Michigan to support research into various aspects of storage subsystem architecture. It includes modules that simulate disks, intermediate controllers, buses, device drivers, request schedulers, disk block caches, and disk array data organizations. In particular, the disk drive module simulates modern disk drives in great detail and has been carefully validated against several production disks (with accuracy that exceeds any previously reported simulator). This manual describes how to configure and use DiskSim, which has been made publicly available with the hope of advancing the state-of-the-art in disk system performance evaluation in the research community. The manual also briefly describes DiskSim's internal structure and various validation results.

This dissertation demonstrates that the conventional approach for evaluating the performance of an I/O subsystem design, which is based on standalone subsystem models, is too narrow in scope. In particular, conventional methodology treats all I/O requests equally, ignoring differences in how individual request response times affect system behavior. As a result, it often leads to inaccurate performance predictions and can thereby lead to incorrect conclusions and poor design choices. A new methodology, which expands the model's scope to include other important system components (e.g., CPUs and system software), is proposed and shown to enable accurate predictions of both subsystem and overall system performance. This dissertation focuses on two specific problems with conventional methodology: 1. Benchmark workloads are often not representative of reality in that they do not accurately reflect feedback effects between I/O subsystem performance (in particular, individual request completion times) and the workload of requests (in particular, subsequent request arrivals). 2. Changes in I/O subsystem performance (e.g., as measured by mean request response times) do not always translate into similar changes in overall system performance (e.g., as measured by mean elapsed times for user tasks). These problems are fundamental to the subsystem-oriented approach and are independent of the model's accuracy. The first problem is illustrated with several examples where commonlyutilized workload generators trivialize feedback effects and produce unrealistic workloads. In each case, quantitative and/or qualitative errors result. The second problem is illustrated with a disk sche...

This paper presents the design of a multimedia storage system for on-demand playback. The design stresses effective utilization of disk bandwidth with minimal data buffer to minimize overall system costs. The design procedure is most distinctive in the following two aspects: 1. It bases on a tight upper bound of the lumped disk seek time for the Scan disk scheduling algorithm to achieve effective utilization of disk bandwidth. 2. It starts with a general two-level hierarchical disk array structure to derive the optimal configuration for specific requirements. Key terms: multimedia, storage system, on-demand playback, disk bandwidth, disk array 1 Introduction In recent years, the design of mass storage systems for multimedia applications has become an active research topic [1, 2, 3, 4, 5, 6, 7]. One of the most This research was sponsored in part by the National Science Council of R.O.C. under grant NSC 83-0408-E-002-002. important applications of multimedia storage systems is on...

A hierarchical storage system achieves scalable storage in providing on-demand video services. In such a system, video files are stored in a tertiary level (such as a library or jukebox), and transferred to a secondary level (such as magnetic disks) from which it is streamed to the users. In this paper, we study the design of such a system for interactive applications in which a movie has to be completely transferred (or "staged") to the secondary level before it is displayed to its user; thereby incurring some user delay. We specify the required storage and bandwidth to meet a delay goal, given application characteristics. We have developed an accurate and yet simple model for the system, which greatly facilitates the design process and allows us to extract important performance characteristics of the system. We provide some design examples, and study the influence of video popularity. Keywords---Hierarchical storage systems, interactive video services, tertiary storage, secondary st...

Video-on-demand (VOD) refers to video services in which users can request any video program from a server at any time. VOD has important applications in entertainment, education, information, and adverstising, such as movie-on-demand, distance learning, home shopping, interactive news, etc. In order to provide VOD services accommodating a large number of video titles and concurrent users, a VOD system has to be scalable --- scalable in storage and scalable in streaming capacity. Our goal is to design such a system with low cost, low complexity, and offering high level of service quality (in terms of, for example, user delay experienced or user loss rate). Storage scalability is achieved by using a hierarchical storage system, in which video files are stored in tertiary libraries or jukeboxes and transferred to a secondary level (of magnetic or optical disks) for display. We address the design of such a system by specifying the required architectural parameters (the bandwidth and storag...

On-demand video servers based on hierarchical storage systems are able to offer highcapacity and low-cost video storage. In such a system, video files are stored in the tertiary level and transferred to the secondary level to be displayed. The design of video servers allowing user interaction with the playbacked video is of great interest. We have conducted a comprehensive study on the architecture and operation of such servers based on hierarchical storage systems for interactive video-on-demand. Our objective is to understand its performance characteristics, so as to design a video server to meet specific application requirements. The applications of interest are many: distance-learning, movie-on-demand, interactive news, home-shopping, etc. The design of such a server actually involves many design choices pertaining to both architecture and operational procedures. As far as architecture is concerned, we need to consider such system parameters as bandwidth, storage capacity, and the ...

This paper proposes a novel data retrieval scheme that achieves effective utilization of disk bandwidth for designing fully interactive video-on-demand systems. The main distinctions of the proposed data retrieval scheme are (1) it requires no extra disk bandwidth to support interactive features such as fast forward search and fast backward search; and (2) it is based on a data placement scheme that can effectively utilize disk bandwidth during normal-speed playback. 1 Introduction In recent years, the design of mass storage systems for video-on-demand (VOD) applications has become an active research topic [1, 2, 3, 4, 5, 6, 7]. In video-on-demand applications, the storage system supports concurrent retrieval of continuous video programs requested by a large number of clients. In order to meet the real-time bandwidth requirement with minimal system costs, the designer must develop appropriate data placement and retrieval strategies so that I/O bandwidth of the storage devices is effe...