Linux File Systems

1. Linux File Systems Introduction to data storage using the ‘msdos’ and ‘ext2’ filesystems

2. Common diskette form-factors • 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

3. Diskettes predominant today • 3-1/2 inch, double-sided high-density • Labeled as: DSHD SS • 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

4. 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

5. Key ‘msdos’ concepts • Record • Cluster • File Directory Entry • File Allocation Table

6. Key ‘ext2’ concepts • Block • Super Block • Block-Group • File Information Node (‘inode’) • Directory Entry (‘dentry’)

7. ‘ext2’ block-size options • # mkfs.ext2 -b 1024 /dev/fd0 • # mkfs.ext2 -b 2048 /dev/fd0 • # mkfs.ext2 -b 4096 /dev/fd0

8. ‘ext2’ disk organization • Boot Block • Super Block • Block-Group Descriptor • Block Bitmap • Inode Bitmap • Inode Table • Root Directory • Data Blocks

9. 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

10. 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