iNode

1. inodes explained
Tutorial 3 - CSCI212
by: Roman Tarnavski

2. Data Blocks
A file system contains ‘blocks’ which hold
data called inodes. A inode describes a
single file in the file system. Typical
information described includes, ownership,
modification times, size and permissions. We
call this information meta-data.
Source: CSCI212 Lecture Notes
by: Daniel Saffioti

3. Data Blocks
Data Blocks
The remainder of the file system (larger proportion)
contains data blocks. These store the contents of
files.
Source: CSCI212 Lecture Notes
by: Daniel Saffioti

4. Source: CSCI212 Lecture Notes
by: Daniel Saffioti

5. Your typical inode
Mode
Permissions
Size
Timestamps
Direct Blocks
Single
Double
Triple

6. Direct
Data Block 1
Data Block 2
.
.
Direct .
Direct Data Block 3
Direct
Direct
Direct
Direct
Direct
Direct
Direct
Direct
Direct
Direct
Single
Double
Triple

7. Single
Direct Data Block 1
Direct Data Block 2
Direct
Direct
Direct Data Block 2048
Direct
Direct Address 1
Direct Address 2
Direct .
.
Direct .
Direct Address 2048
Direct
Single
Double
Triple

8. Double
Direct Data Block 1
Direct Data Block 2
Direct
Direct Address 1
Direct Address 2 Data Block 2048
Direct .
.
Direct Address 1 .
Direct Address 2 Address 2048
Direct . Data Block 1
.
Direct . Data Block 2
Direct Address 2048
Direct
Address 1
Single Data Block 2048
Address 2
Double
.
Triple .
.
Address 2048

9. Triple
Data Block 1
Data Block 2
Direct
Direct Address 1
Address 2 Data Block 2048
Direct
Direct .
.
Direct Address 1 Address 1 .
Direct Address 2 Address 2 Address 2048
Direct . . Data Block 1
. .
Direct
. . Data Block 2
Direct Address 2048 Address 2048
Direct Address 1
Direct Address 2 Data Block 2048
Direct .
.
Single Address 1 .
Double Address 2 Address 2048
Triple .
. Data Block 1
.
Data Block 2
Address 2048
Address 1
Address 2 Data Block 2048
.
Address 1 .
.
Address 2
Address 2048
.
.
.
Address 2048

10. All Together?

11. Data Block 1
Data Block 2
.
.
Direct . Data Block 1
Direct Data Block 3 Data Block 2
Direct
Direct
Direct Data Block 2048
Direct Data Block 1
Direct Address 1 Data Block 2
Address 1
Direct Address 2 Data Block 2048
Address 2
Direct .
. .
Direct . .
.
Direct Address 2048 Data Block 1
Address 2048
Direct Data Block 2
Single
Double Address 1
Triple Data Block 2048
Address 2
Address 1
. Data Block 1
Address 2 .
. Data Block 2
.
. Address 2048
.
Address 2048 Address 1
Address 2 Data Block 2048
.
.
Address 1 Address 1 .
Address 2 Address 2 Address 2048
. . Data Block 1
. .
. . Data Block 2
Address 2048 Address 2048
Address 1
Address 2 Data Block 2048
.
.
Address 1 .
Address 2 Address 2048
.
. Data Block 1
.
Data Block 2
Address 2048
Address 1
Address 2 Data Block 2048
.
Address 1 .
.
Address 2
Address 2048
.
.
.
Address 2048

12. Maximum Size of Direct
Blocks

13. Maximum Size of Direct
Blocks
Where did the 2048 Addresses come from?

14. Maximum Size of Direct
Blocks
Where did the 2048 Addresses come from?
Assuming 32-bit architectures

15. Maximum Size of Direct
Blocks
Where did the 2048 Addresses come from?
Assuming 32-bit architectures
32-bit = 4 bytes (32 / 8)

16. Maximum Size of Direct
Blocks
Where did the 2048 Addresses come from?
Assuming 32-bit architectures
32-bit = 4 bytes (32 / 8)
Thus 8192 [block size] /4 [bytes per addressable block]

17. Maximum Size of Direct
Blocks
Where did the 2048 Addresses come from?
Assuming 32-bit architectures
32-bit = 4 bytes (32 / 8)
Thus 8192 [block size] /4 [bytes per addressable block]
= 2048 Addressable Blocks

18. Questions
What is the maximum possible file size that
can be represented via direct data blocks?

19. Maximum Size of Direct
Blocks
block size
blocks
= 8192 x 12 = 98,304 bytes = 96Kb

20. Maximum FileSize using
First-Indirect Linking

21. Maximum FileSize using
First-Indirect Linking
Direct: 12 blocks @ 8192 bytes (12 x 8192)

22. Maximum FileSize using
First-Indirect Linking
Direct: 12 blocks @ 8192 bytes (12 x 8192)
=96Kb

23. Maximum FileSize using
First-Indirect Linking
Direct: 12 blocks @ 8192 bytes (12 x 8192)
=96Kb
Indirect: 2048 @ 8192 (2048 x 8192) =
16,384 Kb = 16,480 [Inclusive of Direct] = 16.09Mb

24. Maximum using Double
Indirect
16,875,520 x 2048 addressable blocks
= 34,561,064,960 bytes
= 32,960 Mbytes

25. Maximum Filesize
[direct + single + double + triple]
2048 x 32.1875Gb
= 64.375 Tb

26. Overhead

27. Overhead
Wish to store: 8,437,760 bytes

28. Overhead
Wish to store: 8,437,760 bytes
8437760 / 8192 [bytes per block]
= 1030 blocks x 4 bytes [per address]
BUT

29. Overhead
Wish to store: 8,437,760 bytes
8437760 / 8192 [bytes per block]
= 1030 blocks x 4 bytes [per address]
BUT
12 Blocks are stored directly

30. Overhead
Wish to store: 8,437,760 bytes
8437760 / 8192 [bytes per block]
= 1030 blocks x 4 bytes [per address]
BUT
12 Blocks are stored directly
Hence we only have 1018 blocks

31. Overhead
Wish to store: 8,437,760 bytes
8437760 / 8192 [bytes per block]
= 1030 blocks x 4 bytes [per address]
BUT
12 Blocks are stored directly
Hence we only have 1018 blocks
1018 x 4 bytes = 4072 bytes = 3.98Kbytes