This article examines the problem of disk scheduling in a multimedia I/O system. In a multimedia server, the disk requests may have constant data rate requirements and need guaranteed service. We propose a new scheduling algorithm, SCAN-EDF, that combines the features of SCAN type of seek optimizing algorithm with an Earliest Deadline First (EDF) type of real-time scheduling algorithm. We compare SCAN-EDF with other scheduling strategies and show that SCAN-EDF combines the best features of both SCAN and EDF. We also investigate the impact of buffer space on the maximum number of video streams that can be supported. We show that by making the deadlines larger than the request periods, a larger number of streams can be supported.We also describe how we extended the SCAN-EDF algorithm in the PRISM multimedia architecture. PRISM is an integrated multimedia server, designed to satisfy the QOS requirements of multiple classes of requests. Our experience in implementing the extended SCAN-EDF algorithm in a generic operating system is discussed and performance metrics and results are presented to illustrate how the SCAN-EDF extensions and implementation strategies have succeeded in meeting the QOS requirements of different classes of requests.
In this paper, we look at the various I/O issues in a multimedia system. In a multimedia server, the disk requests may have constant data rate requirements and need guaranteed service. We study the impact of the real-time nature of the I/O requests on the various components of the I/O system. We study the impact of disk scheduling algorithms on the performance of a multimedia system. We investigate the impact of bu er space on the maximum number of video streams that can be supported. We show that by making the deadlines larger than the request periods, a larger number of streams can be supported. We also show how deadline extension helps in utilizing multiple disks on a single SCSI bus.
A bstvactThis paper presents an architecture for a file service capable of supporting a very large number of users and providing for each user a lifetime involvement with the file service, while giving the appearance of a single homogeneous system. The architecture is based on the provision of an independent name space for each user and the use of hints for name resolution.Concern about efficient implementation of the architecture leads to the support of file caching and the use of server callbacks to aid in maintaining cache consistency. Updatein-place semantics are provided for those applications that require direct access to localized parts of files, but particularly efficient cache validation strategies encourage the use of immutable files. All file service metadata are updated in atomic and recoverable ways using write-ahead logging. The file service also supports user-level distributed atomic actions based on a two-phase commit synchronization protocol.The file service supports user and resource reassignments in a location-independent way by employing the system's user location mechanism during file name resolution when hints are invalid. File sharing information remains valid even when participants migrate.
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