A continuum of disk scheduling algorithms
A continuum of disk scheduling algorithms
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DOI：
10.1145/7351.8929
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发表时间：
1987-01
期刊：
影响因子：
--
通讯作者：
R. Geist;S. Daniel
中科院分区：
文献类型：
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作者：
R. Geist;S. Daniel
定义了一个连续的磁盘调度算法V（R），其端点为V（0）= SSTF和V（1）= SCAN。V（R）保持当前的SCAN方向（入或出），并以最小的有效距离服务下一个请求。位于当前方向的请求的有效距离是其与读/写头的物理距离（以柱面为单位）。反向请求的有效距离是其物理距离加上R x（磁盘上的柱面总数）。通过使用模拟方法，它表明，这个定义的连续也提供了一个连续的性能，无论是相对于平均值和相对于标准偏差的请求等待时间。对于作为两个度量μw + kow的线性组合的目标函数，可以看到连续体的中间点提供的性能一致上级SSTF和SCAN。给出了V（R）的一种实现方法及其在真实的系统中的实验结果。
A continuum of disk scheduling algorithms, V(R), having endpoints V(0) = SSTF and V(1) = SCAN, is defined. V(R) maintains a current SCAN direction (in or out) and services next the request with the smallest effective distance. The effective distance of a request that lies in the current direction is its physical distance (in cylinders) from the read/write head. The effective distance of a request in the opposite direction is its physical distance plus R x (total number of cylinders on the disk). By use of simulation methods, it is shown that this definitional continuum also provides a continuum in performance, both with respect to the mean and with respect to the standard deviation of request waiting time. For objective functions that are linear combinations of the two measures, μw + kow, intermediate points of the continuum are seen to provide performance uniformly superior to both SSTF and SCAN. A method of implementing V(R) and the results of its experimental use in a real system are presented.