Lecture 9

Question 1

What does file systems consist of?

Answer 1

A storage service and a directory service

Question 2

What is a storage service?

Answer 2

Clients do not know about physical characteristics of the disks or where on the disk the files have been stored

Question 3

What does a storage service need to make sure of?

Answer 3

That a file is not lost, even if there are hardware failures or software crashes

Question 4

What is a directory service?

Answer 4

Clients can give convenient text names to files and group them in directories

Question 5

What is the purpose of a directory service?

Answer 5

Clients should be able to access the sharing of their files with others by specifying who can access a given file

Question 6

What is a file directory?

Answer 6

A structure associated with any file management system and collection of files

Question 7

What does a file directory contain?

Answer 7

Information about the files. MOST OF INFO HANDLED BY OS. Some information is availiable to users through system routines (the user cannot directly access the directory=

Question 8

When is a tree-structured file system less effective?

Answer 8

When there are a large number of files in a given directory

Question 9

What are the pros of different unit sizes when allocating space for a file?

Answer 9

Fixed-size: Simplify the reallocation of space
Small fixed-size: Reduce wasted space
Lots of small units requires more space for allocation tables

Question 10

What is static allocation?

Answer 10

Declare the max size in advance

Question 11

What are the cons of static allocation?

Answer 11

-May be hard to guess space needed
- Tendency to overestimate space needed

(Only OK if the file will never change)

Question 12

What are some cons of dynamic allocation?

Answer 12

Files are often no longer contiguous

Question 13

What are the three allocation methods?

Answer 13

Contiguous allocation
Chained allocation
Indexed allocation

Question 14

What is contiguous allocation?

Answer 14

A single contiguous. set of blocks assigned to a file when it’s created.

Question 15

What are some pros and cons of contiguous allocation?

Answer 15

Good performance for sequential files
External fragmentation and the need to specify file size at creation

Question 16

How can external fragmentation in contiguous allocation be managed?

Answer 16

By using compaction to combine free space

Question 17

How does chained allocation work?

Answer 17

Each block contains a pointer to the next block, forming a chain

Question 18

What are the benefits of chained allocation?

Answer 18

It is easy to add blocks to a file and is well-suited for sequential access

Question 19

What is a drawback of chained allocation regarding access patterns?

Answer 19

It does not accommodate locality, requiring multiple disk accesses for random blocks

Question 20

What does “file consolidation” mean in the context of chained allocation?

Answer 20

Consolidation is a process using utility software to improve locality for better performance

Question 21

How does indexed allocation work?

Answer 21

A file allocation table contains a separate index for each file, listing the locations of all blocks assigned to the file

Question 22

What types of file access are supported by indexed allocation?

Answer 22

Both sequential and random access

Question 23

What is a key feature of fixed-size blocks in indexed allocation?

Answer 23

They simplify tracking and allocating space for files.