File System Management

Question 1

What are the essential requirements for long-term information storage in a file system?

Answer 1

• Ability to store a large amount of information
• Information must survive process termination
• Concurrent access by multiple processes

Question 2

Define “File” in the context of file systems

Answer 2

A file is an abstraction for a collection of blocks on disk, persistent, named, and provides convenient sequential or random access

Question 3

What is the purpose of the Master Boot Record (MBR) in a file system layout?

Answer 3

The MBR (sector 0) contains information to allow the OS to boot from the disk

Question 4

List the primary file operations

Answer 4

• Create, make a new file
• Delete, remove a file
• Open/Close, manage file metadata in memory
• Read/Write, handle data operations
• Seek, change the current position for access
• Rename, change the file’s name

Question 5

What are the advantages of contiguous file allocation?

Answer 5

• Easy implementation
• Excellent read performance due to minimal seeking

Question 6

What is the main disadvantage of using linked list allocation for file systems?

Answer 6

Random access is very slow because accessing any specific block requires traversing the list sequentially

Question 7

Explain the purpose of i-nodes in file systems

Answer 7

I-nodes store attributes and disk addresses for file blocks, requiring only i-nodes for open files to be in memory

Question 8

What are the two types of file system backups?

Answer 8

1. Full backup, copies the complete state of storage
2. Incremental backup, records only files updated since the last backup

Question 9

How do symbolic links differ from hard links in shared files?

Answer 9

• Symbolic links, point to the pathname of the original file
• Hard links, directly reference the same i-node as the original file

Question 10

What is the trade-off in choosing the block size for disk space management?

Answer 10

Larger block sizes reduce overhead but increase internal fragmentation, while smaller block sizes require more overhead and links

Question 11

How do you calculate Turn-around Time and Waiting Time in scheduling algorithms like FCFS, SJF, Round Robin, and Priority-based?

Answer 11

• Turn-around Time = Completion Time - Arrival Time
• Waiting Time = Turn-around Time - Burst Time

Question 12

How are read and lseek system calls used in UNIX?

Answer 12

• read(fd, buffer, count), reads count bytes from the file descriptor fd into buffer
• lseek(fd, offset, whence), moves the file pointer by offset based on whence (SEEK_SET, SEEK_CUR, or SEEK_END)

Question 13

What is the purpose of the magic number in an executable file’s header in UNIX?

Answer 13

The magic number identifies the file type and format. It is specific and not random

Question 14

Differentiate between internal fragmentation and external fragmentation

Answer 14

• Internal Fragmentation, unused space within allocated blocks
• External Fragmentation, unused space outside allocated blocks due to scattered free memory

Question 15

Compare contiguous allocation, linked list allocation, and table/indexed allocation

Answer 15

• Contiguous Allocation, fast access but prone to fragmentation
• Linked List Allocation, eliminates fragmentation but slow random access
• Table/Indexed Allocation, good random access, requires extra memory for indices

Question 16

How does a bitmap represent free-space management in file systems?

Answer 16

• A bitmap uses bits to indicate block usage: 1 (free), 0 (allocated)
• Writing a file updates free blocks to 0, deleting a file sets blocks back to 1

Question 17

What are the key design issues in selecting block size for a file system?

Answer 17

• Large blocks, fewer disk accesses, more internal fragmentation
• Small blocks, better utilisation, more metadata overhead
• Compromise is based on file sizes and access patterns