. Swap-Space Management . . . . . . . . Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 操作系统原理与设计 第 12 章 Mass-Storage structure （外存） 陈香兰 中国科学技术大学计算机学院 2009 年 09 月 01 日 陈香兰 操作系统原理与设计
. 4 . .. 3 Disk Scheduling . .. Disk Management . . .. 5 Swap-Space Management . .. 6 Disk Structure 2 .. . . . . . Overview of Mass Storage Structure Disk Structure Disk Scheduling Disk Management Swap-Space Management . . .. 1 Overview of Mass Storage Structure 小结和作业 . 提纲 小结和作业 陈香兰 操作系统原理与设计
. . Disks can be removable disk surface Head crash results from disk head making contact with the to rotate under the disk head (rotational latency) arm to desired cylinder (seek time) and time for desired sector Positioning time (random-access time) is time to move disk computer Transfer rate is rate at which data flow between drive and Drives rotate at 60 to 200 times per second computers Magnetic disks provide bulk of secondary storage of modern . Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . Overview of Mass Storage Structure I That ’ s bad 陈香兰 操作系统原理与设计
. . built into drive or storage array Host controller in computer uses bus to talk to disk controller SCSI Busses vary, including EIDE, ATA, SATA, USB, Fibre Channel, Drive attached to computer via I/O bus . Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . Overview of Mass Storage Structure II 陈香兰 操作系统原理与设计
. . . . . . Overview of Mass Storage Structure Disk Structure Disk Scheduling Disk Management Swap-Space Management . 小结和作业 . Overview of Mass Storage Structure III 陈香兰 操作系统原理与设计
. . SDLT Oper Common technologies are 4mm, 8mm, 19mm, LTO-2 and 20-200GB typical storage Once data under head, transfer rates comparable to disk Kept in spool and wound or rewound past read-write head transfer medium between systems Mainly used for backup, storage of infrequently-used data, Access time slow Relatively permanent and holds large quantities of data Was early secondary-storage medium Magnetic tape . Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . Overview of Mass Storage Structure (Cont.) Random access ∼ 1000 times slower than disk 陈香兰 操作系统原理与设计
. . Mapping proceeds in order through that track, then the rest of cylinder. Sector 0 is the first sector of the first track on the outermost Cylinder: track: sector of the disk sequentially. The 1-D array of logical blocks is mapped into the sectors usually, 512B the logical block is the smallest unit of transfer. Disk drives are addressed as large 1-D arrays of logical blocks, . cylinders from outermost to innermost. Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . the tracks in that cylinder, and then through the rest of the 小结和作业 . Disk Structure I 陈香兰 操作系统原理与设计
. . constant Sectors/track 2 . . . Defective sectors 1 . . . However,in practise, the mapping is difficult, because . Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . Disk Structure II 陈香兰 操作系统原理与设计 zones of cylinder
. . Minimize seek time to rotate the desired sector to the disk head. Rotational latency is the additional time waiting for the disk 2 . . . the cylinder containing the desired sector. Seek time is the time for the disk are to move the heads to 1 . . . Access time has two major components this means having a fast access time and disk bandwidth. disk drives, . . . . Overview of Mass Storage Structure Disk Structure Disk Scheduling Disk Management Swap-Space Management . 小结和作业 . Disk Scheduling I The OS is responsible for using hardware efficiently — for the Seek time ≈ seek distance 陈香兰 操作系统原理与设计
. . requests. Several algorithms exist to schedule the servicing of disk I/O empty or not Request queue and the completion of the last transfer. divided by the total time between the first request for service Disk bandwidth is the total number of bytes transferred, . We illustrate them with a request queue ( 0-199 ). Head points to 53 initially Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . Disk Scheduling II 98, 183, 37, 122, 14, 124, 65, 67 陈香兰 操作系统原理与设计
. Disk Scheduling Simplest . . Disk Management Swap-Space Management Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . FCFS Total head movement = Σ ( h i − h i − 1 ) = | 98 − 53 | + | 183 − 98 | + | 37 − 183 | + | 122 − 37 | + | 14 − 122 | + | 124 − 14 | + | 65 − 124 | + | 67 − 65 | = 640 陈香兰 操作系统原理与设计
. position. . . . . Overview of Mass Storage Structure Disk Structure Disk Scheduling Disk Management Swap-Space Management . . Optimal? Selects the request with the minimum seek time from the current head 小结和作业 . SSTF (shortest-seek-time-first) SSTF ≈ SJF : starvation Total head movement = | 65 − 53 | + | 67 − 65 | + | 37 − 67 | + | 14 − 37 | + | 98 − 14 | + | 122 − 98 | + | 124 − 12 | + | 183 − 124 | = 236 陈香兰 操作系统原理与设计
. . Waiting time: Maximum is ? Illustration shows total head movement of 208 cylinders. where the head movement is reversed and servicing continues. other end , servicing requests until it gets to the other end of the disk, The disk arm starts at one end of the disk, and moves toward the . Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . SCAN (elevator algorithm) 陈香兰 操作系统原理与设计
. . the last cylinder to the first one. Treats the cylinders as a circular list that wraps around from requests on the return trip. returns to the beginning of the disk , without servicing any When it reaches the other end, however, it immediately servicing requests as it goes. from one end of the disk to the other. The head moves Provides a more uniform wait time than SCAN. . Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . C-SCAN I 陈香兰 操作系统原理与设计
. . . . . . Overview of Mass Storage Structure Disk Structure Disk Scheduling Disk Management Swap-Space Management . 小结和作业 . C-SCAN II 陈香兰 操作系统原理与设计
. Disk Management way to the end of the disk. then reverses direction immediately, without first going all the Arm only goes as far as the last request in each direction , Version of C-SCAN . . Swap-Space Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . C-LOOK 陈香兰 操作系统原理与设计
. . algorithm. Either SSTF or LOOK is a reasonable choice for the default algorithm if necessary. module of the OS, allowing it to be replaced with a different The disk-scheduling algorithm should be written as a separate The location of directories and index blocks (caching?) the file-allocation method the number and types of requests, which can be influenced by Performance depends on heavy load on the disk. SCAN and C-SCAN perform better for systems that place a SSTF is common and has a natural appeal . Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . Selecting a Disk-Scheduling Algorithm 陈香兰 操作系统原理与设计
. . (From: read and write. disk controller can sectors that the Dividing a disk into Low-level formatting , Disk Formatting . Swap-Space Management Disk Management Disk Scheduling Disk Structure Overview of Mass Storage Structure . . . . 小结和作业 . Disk Management I or physical formatting http://tjliu.myweb.hinet.net/COA CH 7.files/image055.jpg) 陈香兰 操作系统原理与设计
. . . . . . Overview of Mass Storage Structure Disk Structure Disk Scheduling Disk Management Swap-Space Management . 小结和作业 . Disk Management II 陈香兰 操作系统原理与设计
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