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
bennojoy@gmail.com Does operations like read, write etc..

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…
Email: bennojoy@gmail.com
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