File Management

Question 1

File system

Answer 1

–resides on secondary storage (disks)
* Provided user interface to storage, mapping logical to physical
* Provides efficient and convenient access to disk by allowing data to be stored, located retrieved easily

Question 2

File control block (FCB)

Answer 2

Also called File Descriptor is a storage structure consisting of information about a file

Question 3

File System Layers

Answer 3

–Application programs
–Logical file system
–File-organization module
–Basic file system
–IO control
–Devices

Question 4

Application programs

Answer 4

file created by user and giver to logical file system

Question 5

Logical file system

Answer 5

Accepts file name as input and check if file is present in directory structure, if yes it finds the location of the file as well as the logical block member

Question 6

File-organization module

Answer 6

Accepts logical block member as input and it performs a mapping in order to find the physical block member in the hard disk

Question 7

Basic file system

Answer 7

Accepts block member and issues a command to I/O control with help of block member

Question 8

IO control

Answer 8

Accepts commands form basic file system and contains device drivers or driver files which interacts with devices

Question 9

Stream-block translation

Answer 9

is the process by which the file system maps the logical view of the data (the stream) into the physical blocks on the disk.

Question 10

File Control Block (FCB)

Answer 10

– Contains many details about the file:
* typically inode number, permissions, size, dates
* NFTS stores into in master file table using relational DB structures

Question 11

File Descriptor

Answer 11

Maintains information about the
file including:
- External name: symbolic name of the file
- Current state: i.e. open for reading, open for execution, closed, etc.
- Sharable: File is sharable if many processes can have it once
- Owner: identity of file owner
- User: list of processes that have the file open
- Locks: read locks and write locks are used to indicate that the file is open for reading or writing
- Protection setting: file permissions
- Reference count: the number of directories in which the file appear
- Length; time of creation; time of last access, time of last modification, etc.

Question 12

Three classes of users on Unix / Linux

Answer 12

a) owner access 7
b) group access 6
c) public access 1

Question 13

How file system can keep track of allocated blocks to a file

Answer 13

• Contiguous Allocation
• Linked List Allocation
• Index Table Allocation
• UNIX file structure

Question 14

Contiguous Allocation

Answer 14

Maps N logical blocks of the file into N continuously physical blocks

Question 15

Linked allocation

Answer 15

Each file a linked list of blocks

• File ends at nil pointer
• No external fragmentation
• Each block contains pointer to next block
• No compaction, external fragmentation
• Free space management system called when new block needed
• Improve efficiency by clustering blocks into groups but increases internal fragmentation
• Reliability can be a problem
• Locating a block can take many I/Os and disk seeks

Question 16

File-Allocation Table

Answer 16

Uses a table to track the clusters on a storage volume and how those clusters link together through associated directories and files.

Question 17

Indexed Allocation

Answer 17

each file has its own index block, which is essentially a table of pointers. Each pointer in the index block refers to a block on the disk where part of the file’s data is stored.

Question 18

UNIX File Structure

Answer 18

The file manager is configured with 4KB (KBytes) blocks, 12 direct pointers, 1 single indirection, 1 double indirection, and 1 triple indirection. Assume 32-bit system.

Question 19

The directory is organized logically to obtain

Answer 19

– Efficiency – locating a file quickly
– Naming – convenient to users
* Two users can have same name for different files
* The same file can have several different names
– Grouping – logical grouping of files by properties, (e.g., all Java programs, all games, …)

Question 19

Directory Organization

Answer 19

-Single-Level Directory
-Two-Level Directory
-Tree-Structured Directories

Question 20

Single-Level Directory

Answer 20

• Naming problem
• Grouping problem

Question 21

Two-Level Directory

Answer 21

• Path name
• Can have the same file name for different user
• Efficient searching
• No grouping capability

Question 22

Tree-Structured Directories

Answer 22

• Efficient searching
• Grouping capability