General purpose operating systems have been designed to provide fast, loss-free disk service to all applications. However, multimedia applications are capable of tolerating some data loss, but are very sensitive to variation in disk service timing. Present research efforts to handle multimedia applications assume pessimistic disk behaviour when deciding to admit new multimedia connections so as not to violate the real-time application constraints. However, since multimedia applications are ``soft' real-time applications that can tolerate some loss, we propose an optimistic scheme for admission control which uses average case values for disk access. Typically, disk scheduling mechanisms for multimedia applications reduce disk access times by only trying to minimize movement to subsequent blocks after sequencing based on Earliest Deadline First. We propose to implement a disk scheduling algorithm that uses knowledge of the media stored and permissible loss and jitter for each client, in addition to the physical parameters used by the other scheduling algorithms. We will evaluate our approach by implementing our admission control policy and disk scheduling algorithm in Linux and measuring the quality of various multimedia streams. If successful, the contributions of this thesis are the development of new admission control and flexible disk scheduling algorithm for improved multimedia quality of service.

This thesis considers the disk scheduling problem. The problem is investigated in two types of settings: offline and online. We first adopt the traveling salesman problem with time windows in the scheduling literature for solving the offline problem. Then we develop a decision epoch scheme in which offline problems are iteratively used in solving the online problem. We perform an experimental study for our approach and two well-known disk scheduling algorithms, and compare them according to several performance criteria.

Modern disk-storage systems have to accomplish the requirements of a variety of application classes. Applications that process continuous-media data such as video and audio streams require the storage system to guarantee sustained bandwidths. Interactive applications demand the storage system to ensure bounded response times, posing timing constraints on the execution of individual disk requests. Traditional timesharing applications may require both high throughput or overall short response times. With the described applications being more and more used together in todays computing systems, the disk-storage subsystems have to efficiently combine the different requirements of this application mix. In this thesis, I develop the design of a storage system that comprehensively addresses the various challenges posed by including the support for quality-of-service guarantees in disk-storage systems. The presented storage system provides three main properties. First, the admission control includes the support for statistical guarantees to increase the share of the disk bandwidth that can be utilized by the admission control. Second, the disk-request scheduling clearly separates the enforcement of real-time guarantees from the task to establish the optimal execution order of the requests, and it provides a flexible mechanism to combine the execution of requests with different quality-of-service requirements. Finally, the file system addresses both the needs of the former two elements of the storage system and of the various file types used by the applications by providing a flexible block-allocation policy and customized client interfaces. I show the implementation of the presented designs with the DROPS Disk-Storage System and I provide a detailed evaluation based on this implementation.

Modern disk-storage systems have to accomplish the requirements of a variety of application classes. Applications that process continuous-media data such as video and audio streams require the storage system to guarantee sustained bandwidths. Interactive applications demand the storage system to ensure bounded response times, posing timing constraints on the execution of individual disk requests. Traditional timesharing applications may require both high throughput or overall short response times. With the described applications being more and more used together in todays computing systems, the disk-storage subsystems have to efficiently combine the different requirements of this application mix. In this thesis, I develop the design of a storage system that comprehensively addresses the various challenges posed by including the support for quality-of-service guarantees in disk-storage systems. The presented storage system provides three main properties. First, the admission control includes the support for statistical guarantees to increase the share of the disk bandwidth that can be utilized by the admission control. Second, the disk-request scheduling clearly separates the enforcement of real-time guarantees from the task to establish the optimal execution order of the requests, and it provides a flexible mechanism to combine the execution of requests with different quality-of-service requirements. Finally, the file system addresses both the needs of the former two elements of the storage system and of the various file types used by the applications by providing a flexible block-allocation policy and customized client interfaces. I show the implementation of the presented designs with the DROPS Disk-Storage System and I provide a detailed evaluation based on this implementation.