文档介绍：Module 13: Secondary-Storage 二级存储
Disk Structure 磁盘结构
Disk Scheduling 磁盘调度
Disk Management 磁盘管理
Swap-Space Management 交换空间管理
Disk Reliability 磁盘可靠性
Stable-Storage Implementation 稳定存储实现
Tertiary Storage Devices 三级存储设备
Operating System Issues 有关操作系统的问题
Performance Issues 有关性能的问题
Applied Operating System Concepts
Disk Structure 磁盘结构
Disk drives are addressed as large 1-dimensional arrays of logical blocks, where the logical block is the smallest unit of transfer. 磁盘设备是以一种逻辑块的一维大数组的形式编址的,这里的逻辑块是传输的最小单位。
The 1-dimensional array of logical blocks is mapped into the sectors of the disk sequentially. 逻辑块的一维数组映射到磁盘上一些相连的扇区。
Sector 0 is the first sector of the first track on the outermost cylinder. 0扇区是最外边柱面的第一个磁道的第一个扇区。
Mapping proceeds in order through that track, then the rest of the tracks in that cylinder, and then through the rest of the cylinders from outermost to innermost. 数据首先都映射到一个磁道,其余的数据映射到同一柱面的其他磁道,然后按照从外向里的顺序映射到其余的柱面。
Applied Operating System Concepts
Disk Scheduling 磁盘调度
The operating system is responsible for using hardware efficiently — for the disk drives, this means having a fast access time and disk bandwidth. 操作系统有责任高效地使用硬件——对于磁盘设备,这意味着很短的访问时间和磁盘带宽。
Access time has two ponents 访问时间包括两个主要部分
Seek time is the time for the disk are to move the heads to the cylinder containing the desired sector. 寻道时间是指把磁头移到所需柱面的时间。
Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head. 旋转延迟是指等待磁盘上所需要的扇区旋转到磁头下面的时间。
Minimize seek time 最小寻道时间
Seek time seek distance 寻道时间寻道距离
Disk bandwidth is the total number of bytes transferred, divided by the total time between the first request for service and pletion of the last transfer. 磁盘带宽,是用传输的总位数,除以第一个服务请求与最后传输完成之间的总时间。
Applied Operating System Concepts
Disk Scheduling (Cont.) 磁盘调度(续)
Several algorithms exist to schedule the servicing of disk I/O requests. 有几种磁盘I/O请求的服务调度算法
We illustrate them with a request queue (0-199). 我们假设一个请求序列。
98, 183, 37, 122, 14, 124, 65,