双头镜像磁盘的实时调度算法及性能评价

DESIGN AND PERFORMANCE EVALUATION OF REAL TIME DISK SCHEDULING FOR TWO HEADED MIRRORED DISK SYSTEMS

本文对双头镜像磁盘系统模型进行实时扩展，并提出了三种实时调度算法：最早截止期优先算法（ＥＤＦ），可满足的最早截止期优先算法（Ｆ－ＥＤＦ）和忽视超时限请求算法（ＩＧＭ－ＥＤＦ）．这三种算法充分考虑了Ｉ／Ｏ请求的截止期限，使双头镜像磁盘系统能更好地满足实时需求．在进行了性能模拟后，发现实时调度算法比非实时算法能更好地满足实时Ｉ／Ｏ请求的时限要求．三种实时调度算法中，适用于硬实时应用的ＩＧＭ－ＥＤＦ的性能最好，Ｆ－ＥＤＦ算法的性能次之，它适用于软实时环境．

This paper extends the two headed mirrored disk model proposed by author's, and presents a real time model for two headed mirrored disk systems. Non real time disk scheduling algorithms for such disk system have been examined, this paper proposes three real time scheduling algorithms: earliest deadline first(EDF), feasible earliest deadline first(F EDF) and ignore missed deadlines(IGM EDF). These three algorithms take deadlines of I/O requests into consideration, so they are useful in the real time applications. The simulation experiments show that real time algorithms perform better than non real time algorithms when serving real time I/O requests. Among real time algorithms, IGM EDF is the best one when employed in the hard real time environment, F EDF is the next best one, and it is useful in soft real time applications.