CSCI 3500: Studio 20

File Systems

File systems are used to heirarchically organize and store data on storage media such as hard drives, DVDs, and solid-state drives.

In this studio, you will:

1. Analyze the Contiguous file allocation strategy
2. Analyze the Linked-List file allocation strategy
3. Analyze the FAT file allocation strategy
4. Consider how block size affects read system performance

Please complete the required exercises below, as well as any optional enrichment exercises that you wish to complete.

As you work through these exercises, please record your answers in a text file. When finished, submit your work by sending your text file and source code to dferry@slu.edu with the phrase File Systems in the subject line.

Make sure that the name of each person who worked on these exercises is listed in the first answer, and make sure you number each of your responses so it is easy to match your responses with each exercise.

Required Exercises

1. As the answer to the first exercise, list the names of the people who worked together on this studio.

2. Suppose you have a hard drive with 20 blocks of storage. This particular drive uses contiguous allocation with a first-fit method of allocating files. Compute the hard drive layout after the following operations take place:

   Create file A - 5 blocks
   Create file B - 3 blocks
   Create file C - 3 blocks
   Create file D - 5 blocks
   Delete file B
   Delete file C
   Create file E - 4 blocks
   Delete file A
   Create file F - 3 blocks
   

3. Suppose you want to measure the disk fragmentation that has occurred. Looking at the above trace you realize that most files on this system occupy 3 blocks or more. How many free chunks are there of size 2 or less?

4. What percentage of total disk space are these fragmentary chunks?

5. Suppose you have the same hard drive as above, but you've upgraded to a linked-list allocation method. Compute the hard drive layout after the following operations take place:

   Create file A - 2 blocks
   Create file B - 4 blocks
   Create file C - 1 block
   Extend file A by 3 blocks
   Reduce file B by 2 blocks
   Create file D - 5 blocks
   Delete file C
   Delete file A
   Create file E - 4 blocks
   

6. How many chunks are there of size 2 or less?

7. Does it still make sense to measure disk fragmentation in this way?

8. Recall that in a linked-list allocation method each individual block of a file keeps track of the successor block. How many blocks must be read to locate the 3500th byte of file A? Suppose that each block is 1024 bytes.

9. Construct the File Allocation Table (FAT) corresponding to the linked-list allocation above.

10. Suppose you have a 10GB drive (2^30 * 10 bytes). How many entries would a FAT need if the block size is 1KB (2^10), 4KB, and 8KB??

11. How large would the FAT be (in bytes) for each size above if each entry were 3 bytes?

12. On a traditional hard drive with spinning magnetic platters, the time it takes to execute a read is the sum of the seek time and the block read time. The seek time is the amount of time it takes the hard drive to physically locate the requested data, and the block read time is the amount of time it takes the data to be read off the disk. If a file is split across multiple blocks, then the drive must seek to each individual block and read it.

    One study found that the average file size on a Linux system is 2475 bytes long. How long does it take to read the average file on a system with 1024-byte (1KB) block sizes? What about 2048 bytes (2KB) and 4096 bytes (4KB)? Suppose a seek time of 10 microseconds and a block read time of 3 microseconds.

Optional Enrichment Exercises

1. No optional exercises