Linux File Systems
Introduction to data storage using
the ‘msdos’ and ‘ext2’ filesystems
Common diskette form-factors
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Package sizes: 8-inch, 5.25-inch, 3.5-inch
Single-sided, Double-sided
Hard-sectored, Soft-sectored
Recording densities:
– Single-density
– Double-density
– High-density
– Ultra high-density
– Super high-density
Diskettes predominant today
• 3-1/2 inch, double-sided high-density
• Labeled as: DSHD SS
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512 bytes-per-sector
18 sectors-per-track
2 tracks-per-cylinder
80 cylinders-per-disk
Total disk capacity: 80 x 2 x 18 x 512 = 1440KB
Formatting a DSHD diskette
• With Linux: a two-step procedure
• 1) Low-Level Formatting:
• root# fdformat /dev/fd0H1440
• 2) High-Level Formatting:
• root# /sbin/mkfs.ext2 /dev/fd0
or
• root# /sbin/mkfs.m sdos /dev/fd0
Key ‘msdos’ concepts
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Record
Cluster
File Directory Entry
File Allocation Table
Key ‘ext2’ concepts
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Block
Super Block
Block-Group
File Information Node (‘inode’)
Directory Entry (‘dentry’)
‘ext2’ block-size options
• # mkfs.ext2 -b 1024 /dev/fd0
• # mkfs.ext2 -b 2048 /dev/fd0
• # mkfs.ext2 -b 4096 /dev/fd0
‘ext2’ disk organization
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Boot Block
Super Block
Block-Group Descriptor
Block Bitmap
Inode Bitmap
Inode Table
Root Directory
Data Blocks
Mounting and Unmounting
• $ mkdir floppy
• # /bin/mount –t msdos /dev/fd0 floppy
• # /bin/mount –t ext2 /dev/fd0 floppy
• # /bin/umount /dev/fd0
• # /bin/umount floppy
Class Exercise
• Use ‘fileview.cpp’ application:
$ fileview /dev/fd0
• Find the location of the ‘super’ block
Look for SUPER_MAGIC: 0xEF53
• Repeat for each ‘ext2’ block-size:
1K, 2K, and 4K