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Homework Assignment #4

Homework Assignment #4. J. H. Wang Nov. 19, 2008. Homework #4. Chap.11: 11.2, 11.6 Chap.12: 12.2, 12.6, 12.8 Due: three weeks ( Dec. 15, 2008 ). Chap.11 11.2: What are the advantages of the variant of linked allocation that uses a FAT to chain together the blocks of a file?

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Homework Assignment #4

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  1. Homework Assignment #4 J. H. Wang Nov. 19, 2008

  2. Homework #4 • Chap.11: 11.2, 11.6 • Chap.12: 12.2, 12.6, 12.8 • Due: three weeks (Dec. 15, 2008)

  3. Chap.11 • 11.2: What are the advantages of the variant of linked allocation that uses a FAT to chain together the blocks of a file? • 11.6: In what situations would using memory as a RAM disk be more useful than using it as a disk cache?

  4. Chap.12 • 12.2 Suppose that a disk drive has 5000 cylinders, numbered 0 to 4999. The drive is currently serving a request at cylinder 143, and the previous request was at cylinder 125. The queue of pending requests, in FIFO order, is 86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130 Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests, for each of the following disk-scheduling algorithms?(a) FCFS(b) SSTF(c) SCAN(d) LOOK(e) C-SCAN(f) C-LOOK

  5. 12.6: Disk I/O requests are not usually uniformly distributed. For example, a cylinder containing the file system FAT or inodes can be expected to be accessed more frequently than a cylinder that only contains files. Suppose you know that 50 percent of the requests are for a small, fixed number of cylinders.(1) Which of the following disk scheduling algorithms would be particularly good for this case? (a) FCFS (b) SSTF (c) LOOK (d) SCAN (e) C-LOOK (f) C-SCAN. Explain your answer. (2) Do you think there is a disk scheduling algorithm that gives even better performance by taking advantage of this “hot spot” on the disk? If yes, please explain your algorithm.(3) Files systems typically find data blocks via an indirection table, such as a FAT in DOS or inodes in UNIX. Describe one or more ways to take advantage of this indirection to improve disk performance.

  6. 12.8: Compare the throughput achieved by a RAID Level 5 organization with that achieved by a RAID Level 1 organization for the following:(a) Read operations on single blocks.(b) Read operations on multiple contiguous blocks.

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