Disk scheduling in a multimedia I/O system

Abstract

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.

An Improved Group-EDF: A Real-Time Disk Scheduling Algorithm

“…When deadlines of two transactions are same then we applies this algorithm [4]. According to it, transactions with the same deadline are arranged using scan algorithms.…”

Scalable multimedia disk scheduling

“…Although EDF achieves good results in terms of minimizing the deadline losses, it degrades the disk utilization, where it does not take into account the cylinder position of disk requests. Many variants of the traditional SCAN algorithm [7] are proposed (e.g., see [1,11,20]) to handle real-time disk requests. The FD-SCAN (Feasible Deadline SCAN) algorithm [1] differs from SCAN in the way that it dynamically adapts the scan direction towards the request with the earliest feasible deadline.…”

“…A deadline is said to be feasible if FD-SCAN estimates that the dead- line can be met. SCAN-EDF [20] achieves a trade-off between the SCAN and EDF algorithms. where requests are served according to their deadlines.…”

“…Two-dimensional disk schedulers are special cases from the Cascaded-SFC disk scheduler by ignoring two of the three stages. For example, FD-SCAN [1], SCAN-EDF [20], multi-queue disk scheduler [4] can be realized by the Cascaded-SFC disk scheduler when using only SF C 3 . The Sweep SFC is used as SF C 3 where the y dimension represents the deadline (for FD-SCAN and SCAN-EDF) or the request priority (for multi-priority scheduling) while the x dimension represents the difference in cylinders between the current cylinder position and the disk request in any direction (for FD-SCAN) or in the current direction (for SCAN-EDF and multi-priority scheduler).…”

“…In attempting to satisfy multiple concurrent and conflicting requirements (e.g., disk bandwidth, deadline, and priority), scheduler designers and algorithm developers depend mainly on heuristics to code the schedulers (e.g., see [1,2,3,5,6,9,12,14,17,20,21]). It is not always clear that these schedulers are equitable to all aspects of the system, or are controllable in a measurable way to favor one aspect of the system over the other.…”