The document discusses the anatomy of file systems and how they are organized on hard disks. It explains that file systems organize scattered data using indexes containing metadata and data blocks containing file contents. File system blocks are mapped to disk blocks using logical block addressing. File systems use inodes to store file and directory metadata, with each file or directory having a corresponding inode containing attributes like owner, size, and pointers to data blocks. Block groups contain groups of inodes and data blocks to organize the file system layout on disk.

1. Anatomy of Filesystems..

2. Anatomy of Hardisks
Track 1 “Platter” – A circular piece of
magnetic material
“Tracks” – Platters divided into
concentric circles
Track 0
Read/Write Head 0
Platter1,track0
Read/Write data from Hardisk ? Platter2,track0 Cylinder 0
Read Cylinder
0,head 0, Platter3,track0
sector 0.
Disk Controller.
CHS Addressing
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3. Anatomy of Communication
Communication in Humans:
Requirements:
• Speaker/Listener
• Voice/Language
• Medium: Air
• Addressing
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4. Communicating with your Hardisk
Various communication standards exist to talk to our Harddisks:
Communication Requirements SCSI Specification
Speaker/Listener Initiator/Target
Voice/Language SCSI Commands
Medium SCSI Bus
Addressing SCSI ID
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5. SCSI Overview
Target Host Bus Adapter(HBA)
ID: 0 8 Bit wide wires
Target SCSI Bus Converts: PCI -Bus
PCI -> SCSI CPU
ID: 1 Initiator
Target
ID: 7
Logical Block Addressing (LBA) – A Data Addressing Standardization:
Block 0/1 Block 2/3
Track 0 Track 1
Sector 0 Sector 1 Sector 0 Sector 1
SCSI Command
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6. SCSI Communication in Action
OS: CPU: Give me Block 1, from disk0
OS: your
data, ”Hello” CPU HBA: Give me Block 1, From Disk 0
CPU: Your data “Hello”
Bus Adapter:
Initiator Hey, Disk 0, I Need your attention
Thanks, READ LBA 2 for me
Ok Bus, You have my attention
Converts LBA 2 –> CHS 0/0/1 Target Disk0
Ok, Here is LBA 2 Data: “Hello” ID 0
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7. FileSystems
Organize Scattered Data:
Visible part of Metadata:
For FileSystems:
• Index(TOC) = Metadata
• Contents = Data
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8. FileSystems - Dig Deeper
FileSystem Blocks:
FileSystem Block Block 0 (4Kb, Block size)
SCSI Block (LBA) Block 0 Block 1 Block … Block 8
Disk Block Sector 0 Sector 1 Sector … Sector 8
Fileystem layout on Disk:
Boot
Block Group 0 Block Group… Block Group .. N
Block
Block 0 Block 1 Block 2 Block 3 Block 4 Block N
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9. FileSystems – Contd…
Block Groups:
Block Group 0
Super Group Descriptor Inode
Data Blocks … N
Block Blocks.. Blocks
Inodes :
Every file or Directory will have a corresponding Inode, which contains information
corresponding to the file or directory Entries in an Inode :
Inode Block: Owner
Inode 1 Mode (permission/Directory/File)
128 bytes
TimeStamp
Inode 2
Address of 1st Data Block
Inode … Address of 2nd Data Block
Inode 32 Address of Direct and Indirect Data Block
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10. FileSystems – Contd…
Difference between file and directory Inode:
File Inode : Data Block 22:
Owner
Hello
Mode (File)
World !
TimeStamp
Data Block 22
Address of 2nd Data Block
Address of Direct and Indirect Data Block
Directory Inode : Data Block 50:
Owner
Mode (Directory) “File1” - 32
TimeStamp “File2” - 36
Data Block 50
Address of 2nd Data Block
Address of Direct and Indirect Data Block
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11. FileSystems – Contd…
SuperBlock :
Free Blocks
Free Inodes
Size
Block Size etc..
Group Descriptor :
Block Number of First Inode
No of free blocks in group
Revisit the FileSystem Layout in Disk:
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12. FileSystem in Action
Listing Contents of a file:
• Read the inode entry of / (Root
directory)
• The root inode is fixed, inode entry 2
in the first inode block of the first
blockgroup
Test Inode
Mode (Directory) “a” – Inode(5)
Data Block 2
Root Inode
Mode (Directory) A Inode “Test” – Inode(3) “hello world”
Mode (File)
“Bin” – Inode(4)
Data Block 1
Data Block 3
Inode1 Inode2 Inode3 Inode4 Inode5 Block1 Block2 Block3 Block4 Block5
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13. Thank You…
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