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The instructions and questions for homework 6 in the cs433: computer systems organization course, which covers topics such as disk performance, i/o performance, and reliability. Students are required to calculate average search times for sequential and binary search, determine the number of transactions per second for different disk choices, and calculate the reliability of an i/o subsystem.
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CS433: Computer Systems Organization Fall 2008
Homework 6
Assigned: Nov/
Due in class Dec/
Total points: 40 points.
Instructions:
Please write your name, NetID and an alias on your homework submissions for posting grades
(If you don’t want your grades posted, then don’t write an alias). We will use this alias
throughout the semester. Homeworks are due in class on the date posted.
1. Disk Performance [10 points] Consider the following hard drive: Seek Time 8 ms Rotation Speed 7200 rpm Transfer Rate 80 MB/s Controller Overhead 0.1 ms Sector Size 512 Bytes
(a) We have a 1 MB binary file stored on a single track. The file contains sorted key/value pairs. Each pair consists of two integers. The first integer is the key and the second is its corresponding value. Integers are 4 bytes long. Assuming the integer key we are searching for is contained within the file, calculate the average time needed to find its corresponding value using sequential search. Assume the only significant factor in the search time is the time to transfer sectors from disk (once transferred to memory, the time needed for to process each record is negligible).Assume we can process the file as we read. On average, how long does it take to find a key/value pair on the hard disk? [6 points]
(b) What would be the worst case time needed if we used binary search? [4 points]
(c) How many hard drives would be required if we use enough small disks such that the hard drives are not the bottleneck? What is the cost of the system? [3 points]
(a) What is the MTTF of the entire I/O subsystem? [4 points]
(b) The owner of the computer system wants more space and performance and decides to double the number of hard disks and put all the disks under RAID 0 (no redundancy). What is the MTTF for the new I/O subsystem? Note, we’ll naturally also be adding 4 IDE cables for the 4 new hard disks too. [3 points]
(c) After taking cs433, the owner of the computer system is more concerned with the reliability of his system and decides to use RAID3 on his 6 hard disks. Assuming a working hot swap drive is available at all times, and it takes 1 hour to reconstruct the data onto this new replacement drive. What is the mean time till data loss? Assume the error we are concerned with is when a drive fails and during the reconstruction, when the RAID system is vulnerable to data loss, another of the drives fails. [3 points]
