CSE 2312 - Assignments

Not Graded Practice for Assignment 4

This is a set of practice questions. Feel free to work on these questions, and to ask questions if you face any difficulties in coming up with answers. While collaboration with others on the graded homework is strictly prohibited, you are free to work on these practice questions together with other people.

Since they are practice questions, you do not have to, and should not, submit answers to these questions on Blackboard. These questions will not be considered in any way towards your course grade. At the same time, based on the instructor's experience, individuals spending substantial and systematic effort in answering these practice questions by themselves tend to significantly improve their overall class performance.


Practice Question 1

(This is Problem 19 from Chapter 2 of the textbook).

Imagine you are writing the disk-management part of an operating system. Logically,you represent the disk as a sequence of blocks, from 0 on the inside to some maximum on the outside. As files are created, you have to allocate free sectors. You could do it from the outside in or the inside out. In terms of disk performance, does it matter which strategy you choose on a modern disk? Explain your answer.


Practice Question 2

(This is Problem 20 from Chapter 2 of the textbook).

How long does it take to read a disk with 10,000 cylinders, each containing four tracks of 2048 sectors? First, all the sectors of track 0 are to be read starting at sector 0, then all the sectors of track 1 starting at sector 0, and so on. The rotation time is 10 msec, and a seek takes 1 msec between adjacent cylinders and 20 msec for the worst case. Switching between tracks of a cylinder can be done instantaneously.


Practice Question 3

(This is Problem 27 from Chapter 2 of the textbook).

You are part of a top-secret international scientific team which has just been assigned the task of studying a being named Herb, an extra-terrestrial from Planet 10 who has recently arrived here on Earth. Herb has given you the following information about how his eyes work. His visual field consists of about 108 pixels. Each pixel is basically a superposition of five "colors" (i.e., infrared, red, green, blue, and ultraviolet), each of which has 32 intensities. The time resolution of Herb's visual field is 10 msec. Calculate the data rate, in GB/sec, of Herb's eyes.


Practice Question 4

Mr. Hacker does not like the fact that he has to buy preconfigured RAID systems. He decides to write software that makes a RAID-5 out of ANY set of disks, as long as each of those disks has the exact same data capacity. This way, the user can buy individual disks, and using Mr. Hacker's software they can use these disks as a RAID. Can Mr. Hacker succeed?

Mr. Hacker's enemy, Mr. Nemesis, predicts that Mr. Hacker will fail. He starts developing a rival software, that can also make a RAID-5 out of a set of disks that the user provides, but makes additional requirements that the set of disks must satisfy. What additional requirements does Mr. Nemesis need to make, to have a successful product?


Practice Question 5

A company has a number of RAID-5 arrays. Each array has 10 disks. On average, a disk fails every 20,000 hours. When a disk fails in a RAID-5 array, it takes one hour to fix the array. Fixing the array involves taking out the broken disk, putting in a new disk, and storing the right data on the new disk. If, during that hour, another disk fails on the array that is getting fixed, the data on the array is lost.

Under these assumptions: suppose that you are fixing an array that had a broken disk. What is the probability that, while you are fixing that array, the array's data will be lost?


Back to the list of assignments.