M13: The OS File System

Question 1

fseek() :

Answer 1

sets the position of the stream to the given offset, allowing
seeking a specified part of the file

Question 2

disk block

Answer 2

basic logic unit of storage on disk of a contiguous set of bytes

Question 3

Disk partitions:

Answer 3

logical split of the actual disk drive. The operating system views each partition as a distinct disk, and different operating systems may be run in each split; each partition has at least one directory, in which all the partition’s files are listed.

Question 4

The typical internal structure of the disk partition includes:

Answer 4

Boot block
Superblock
Free space data structure
i-node list

Question 5

Boot block:

Answer 5

contains information on the disk layout and code for loading the operating system into the kernel space

Question 6

Superblock:

Answer 6

contains basic information about the file system, including
the file system size, list of free blocks, list of allocated blocks, and time of the last modification to the partition; the superblock can be read into
memory at boot time

Question 7

Free space data structure:

Answer 7

tracks the free blocks in the disk

Question 8

I-nodes list :

Answer 8

stores information about the individual files stored on disk, and allocatable blocks for directories and file systems

Question 9

Master boot record :

Answer 9

stores information about the entire drive

Question 10

Partition table:

Answer 10

specifies the beginning of each partition

Question 11

Disk space allocation

Answer 11

managing data in the disk with the aims to ensure fast

sequential access, fast random access, the ability to grow a file system quickly, and to minimize fragmentation

Question 12

Contiguous allocation :

Answer 12

each file occupies a contiguous region of blocks

Question 13

Linked-list allocation :

Answer 13

hold a linked list of blocks for each file such that

each block contains a pointer to the next block

Question 14

File allocation table :

Answer 14

stores a condensed version of the linked list to be
stored at the beginning of the file system; the file is stored in allocated
clusters

Question 15

Linked list with indexing or i-nodes

Answer 15

supports direct access to the file’s

blocks by storing files in the i-node data structure

Question 16

i-node (index node) :

Answer 16

kernel structure storing information about
each file in the file system; contains a pointer to the disk blocks
containing the file’s data, and information such as the file
permissions, ownership, modification time, and file type

Question 17

directory

Answer 17

file that holds the list of filenames and their inodes; provides
information needed to find the disk data blocks of a file

Question 18

Hard links:

Answer 18

to represent two different paths for a file, create a single i-node and
have two directory entries that point to the same i-node; relies on the link-counter

Question 19

Link-counter:

Answer 19

counts the number of ways that an i-node can be retrieved

along different paths

Question 20

Symbolic/soft link:

Answer 20

the original file has its own i-node and for each reference or
path to the file, there is a separate i-node, of type LINK, for a file that just
contains the path name to the original file

Question 21

Free space management:

Answer 21

tracking unallocated blocks in a portion of the disk
partition
Approaches: A) Bitmap B) Linked List

Question 22

Bitmap - free space management

Answer 22

maintains for the entire disk partition with one encoding the fact
that the block of a particular number is free and zero otherwise

Question 23

Linked list:

Answer 23

list storing the free blocks

Question 24

In-memory cache :

Answer 24

uses a scheme to store blocks that are likely to be requested
from disk, to shortcut the need for a disk search and propagate the data to the
requesting process

Question 25

LRU scheme :

Answer 25

given the limited in-memory cache size, evicts the least

recently used block from the cache when new blocks are being added in

Question 26

Incremental backups :

Answer 26

every time you synchronize with your server, it will only

backup files that have been changed since the last time

Question 27

Physical backup:

Answer 27

physically copy block by block from one disk to another

Question 28

Logical backup:

Answer 28

copies files from one disk to another