Homework 12: Chapter 12 Questions

Due: Thursday, April 19th by 5:59 PM

Header

Please put the following at the top of a flat text file, hwk12.txt:

Homework Questions

Write the answers to the following questions in hwk12.txt:
  1. The suitability of a storage device for random access depends on the transfer size. The term "streaming transfer rate" denotes the rate for a data transfer that is underway, excluding the effect of access latency. By contrast, the effective transfer rate is the ratio of total bytes per total seconds, including overhead time such as access latency. Suppose that a magnetic disk has an access latency of 15 milliseconds and a streaming transfer rate of 5 megabytes per second.
    1. Random access causes the effective transfer rate of a device to decrease, because no data are transferred during the access time. For the disk described, what is the effective transfer rate for the following size transfers (in MB/sec)?
      • 512 B
      • 8 KB
      • 1 MB
      • 16 MB
    2. The utilization of a device is the ratio of effective transfer rate to streaming transfer rate. Calculate the percentage of utilization of the disk drive for each of the four transfer sizes given in part a.
    3. Suppose that a utilization of 25 percent (or higher) is considered acceptable. Using the performance figures given, compute the smallest transfer size for disk that gives acceptable utilization.
  2. The Hadron Collider produces approximately 1 petabyte of data per second.
    1. How many exabytes of data does it produce everyday?
    2. How many 1 terabyte drives would be needed to store the data for 1 day?
    1 terabyte = 240 bytes
    1 petabyte = 250 bytes
    1 exabyte = 260 bytes
  3. 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?
    1. FCFS
    2. SSTF
    3. LOOK
    4. C-LOOK
  4. What is the average rotational latency in milliseconds of the following disk drives:
    1. 7200 RPM
    2. 10000 RPM
    3. 15000 RPM
  5. The reliability of a hard-disk drive is typically described in terms of a quantity called mean time between failures (MTBF). Although this quantity is called a "time," the MTBF actually is measured in drive-hours per failure. If a disk farm contains 1000 drives, each of which has a 750,000-hour MTBF, which of the following best describes how often a drive failure will occur in that disk farm: once per thousand years, once per century, once per decade, once per year, once per month, once per week, once per day, once per hour, once per minute, or once per second?
  6. What kind of secondary storage device do you primary use? What is its transfer rate and average seek time, etc.?

Submission

Submit hwk12.txt using the handin program. For example, for this homework, type the following in a terminal exactly as it appears: 
  handin  hwk12  hwk12.txt

Alternatively, you can submit the assignment from any computer via PeerSpace. After successfully logging into PeerSpace, go to Tools, then Assignments. Click on the Submit link.