📜  SSTF和LOOK磁盘调度算法之间的区别

📅  最后修改于: 2021-08-27 07:13:47             🧑  作者: Mango

1. SSTF磁盘调度算法:
SSTF代表最短搜索时间优先。顾名思义,该算法为最接近头部或指针当前位置的任务请求提供服务。在这里,头部的方向在确定整体头部运动中起着至关重要的作用。如果请求之间出现平局,那么头部将按照其进行中的方向处理遇到的请求。

例子 –
请考虑具有200个磁道(0-199)的磁盘和具有I / O请求的磁盘队列,其顺序如下:98、183、40、122、10、124、65。Read \ Write的当前磁头位置头是53,并且将向右移动。使用SSTF算法计算读/写磁头的磁道移动总数。

头部总动作

= (65-53)+(65-40)+(40-10)+(98-10)
              +(122-98)+(124-122)+(183-124)
= 240 

2. LOOK磁盘调度算法:
外观算法实际上是SCAN算法的改进版本。在这种算法中,磁头从磁盘的一侧开始第一个请求,并通过为磁盘之间的所有请求提供服务而朝另一端移动。与SCAN不同,在这种情况下,磁头不是一直走到最后一个轨道,而是一直走到最后一个请求,然后改变方向。与SSTF不同,它不处理最接近头部或指针当前位置的任务请求。

例子 –
请考虑具有200个磁道(0-199)的磁盘和具有I / O请求的磁盘队列,其顺序如下:98、183、40、122、10、124、65。Read \ Write的当前磁头位置头是53并且将向右移动。使用LOOK算法计算读/写磁头的磁道移动总数。

头部总动作

= (65-53)+(98-65)+(122-98)
              +(124-122)+(183-124)+(183-40)+(40-10)
= 303 

SSTF和LOOK磁盘调度算法之间的区别:

LOOK SCHEDULING ALGORITHM SSTF SCHEDULING ALGORITHM
1. The performance of LOOK is better than SSTF. SSTF lags in performance.
2. LOOK results in increased total seek time. It reduces total seek time as compared to LOOK.
3. It provides low variance in average waiting time and response time. This algorithm provides high variance average response time and waiting time.
4. As shown in above example, direction of head gets reversed when it serves the last request in one direction. But here, direction of head plays an important role, in order to break tie between requests.
5. In this algorithm, there is an overhead for finding end request. Here, there is an overhead for finding out closest request.
6. LOOK does not cause starvation to any request. Here, the request which are far from head will suffer starvation.
7. LOOK algorithm can handle requests more effectively than SSTF. Here handling of request is not so good as compared to LOOK algorithm.