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Comp111 Final Exam
Dec 14, 2017 - open books and notes

No electronic devices of any kind allowed, including cellphones, calculators, pagers, etc. Please turn these off before beginning the exam.

Please show all work on these pages. Feel free to use the backs of pages as appropriate. Make sure that your work for each problem is clearly marked. Please place your name on each sheet.

Please note that the amount of space after each question does not indicate length requirements for an answer! If an answer is short, write it succinctly.

These pages will be graded and returned electronically, like exercises.

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  1. Explain how a single linux file can have more than one pathname.























  2. Can a file with more than one pathname be accessible via one pathname and not accessible via another? Why?

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  3. Why is there a copy of the superblock in every inode group of a filesystem?























  4. Under what conditions can one lose files with journalling in effect? Why?

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  5. If the average time between entering and exiting a restaurant is two hours, and the average arrival rate is 20 customers per hour, what is the average number of people in the restaurant at a time?























  6. If there are an average of 200 people in another restaurant, and the average time between entering and exiting the restaurant is 2 hours, then what is the arrival rate for people coming to the restaurant?

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  7. Suppose we decide to split up a disk journal into several separated block groups distributed throughout a disk. Is this advantageous? Why or why not?























  8. In the command mkfs, there are a lot of options for constructing a filesystem. What happens if block groups in a filesystem are made too small? What if they are made too large?

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  9. One of the grand challenge problems of cloud computing is the zero-latency failover problem: how can one keep two computers so closely synchronized that one can replace the other quickly and completely? This, of course, includes disk contents. Describe how disk journals could help with this problem. How would you use journals, and what would be the limits of the solution?























  10. There were difficulties in Assignment 3 with setting some limits, because the limits could prevent the child process from running at all. Why?

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  11. (Extra Credit) The library functions fsync and fdatasync ensure that the memory pages for a file are posted to disk, and mark the memory pages as "clean" rather than dirty, but do not de-allocate the pages. Why is this a good design?