Probably the most important issue in implementing file storage is keeping track

Question

Probably the most important issue in implementing file storage is keeping track of which disk blocks go with which file. Which of the statements below are true about the methods used for that?

i the simplest allocation scheme is to store each file as a contiguous run of disk blocks; the advantage of this method is that there is no disk fragmentation

ii we can store each file as a linked list of disk blocks, using the first word in each block as a pointer; a disadvantage of this method is that random access is extremely slow (resolved by placing the pointers in a table in memory)

iii the File Allocation Table (FAT) scales well to large disks

iv we can associate each file with a data structure called an i-node (index node), which lists the attributes and disk addresses of the file’s blocks; this method occupies less space than the FAT

ii and iv

Making the file system work is one thing; making it work efficiently and robustly in real life is another thing. What are some of the issues involved in managing disks?

i choosing the block size – small blocks are bad for performance, but good for disk space utilization

ii free space management – using linked list or a bitmap

iii disk compaction and defragmentation – a fast algorithm for reducing wasteful fragmentation must be implemented such as Vogels, 1999

iv setting up a quota for each user – to prevent users from using up too much disk space

Accessing disk is much slower than accessing memory. As a result, many file systems have been designed with various optimizations to improve performance. What is an example of file system performance optimization?

Explanation / Answer

1. ii and iv

2. ii, iii, and iv

3. c)reducing disk arm motion – i.e. try to get blocks into the cache before they are needed

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