1 Million Mtbf For A Disk Drive example essay topic
466 words
From Elementary physics, we know that, when an object is subjected to a constant acceleration a, the relationship between distance d and time t is given by d = 1/2 at 2. Suppose that, during a seek, the disk in Exercise 13.2 accelerates the disk arm at a constant rate for the first half of the seek, then decelerates the disk arm at the seek rate for the second half of the seek. Assume that the disk can perform a seek the an adjacent cylinder in 1 millisecond, and a fill-stoke seek over all 5000 cylinders in 18 milliseconds. a. The distance of a seek is the number of cylinders that the head moves. Explain why the seek time is proportional to the square root of the seek distance. The head accelerates and decelerates and the same constant for equal amounts of time. Therefore we can rewrite the equations d = 1/2 t 2, or ( (d 2) 1/2) = t. b. Write and equation for time as a function of distance. ( (d 2) 1/2) = t. c. Calculate the total seek time for each of the schedules in Exercise 13.2. Determine which schedule is the fastest (has the smallest total seek time). The percentage speedup is the time saved divided by the original time. What is the percentage speedup of the fastest schedule over FCFS?
327.8-137.2 = 190.6190. 6/327.8 = . 58 or 58%13.16 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 call a "time", the MTBF is measured in drive-hours per failure. a. If a system contain 1,000 disk 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 pre week, once per minutes, or once per second?
750,000 drive-hours per failure / 1,000 drives = 7500 hours per failure or 313 days per failure. Once per year. b. Mortality statistics indicate that, on the average, a U.S. resident has about a 1 in a 1000 chance of dying between ages 20 and 21 years. Deduce the MTBF hours for 20 year olds. Convert this figure from hours to years.
What does this tell us? c. Manufacture claims a 1-million MTBF for a disk drive. What can you conclude about the number of years for which one of these drives is under warrantee? 1,000,000 drive-hours per failure / 24 hours = 41,667 / 365 = 114 years between failures.
