Linux Level 2 Student Manual
The ext2 and ext3 filesystems have similar organizational structures. Both filesystems consists of the following components:
Superbock
Group Blocks
Backup Superblocks
Inode Tables
Data blocks
In this section we will cover these components.
Note: The “disk label” (partition table) and “boot sector” (where a boot loader can be stored) are components that you will see described as part of a partition. They are not, however, part of the filesystem, and will not be covered in great detail in this module.
Groups
For organizational reasons, the partition is divided into cylinder groups. Typically there are 16 cylinders per group, but there is a configuration option to allow for different sizes in the mke2fs command.
Superblock
The superblock contains information about the partition itself. This information includes:
FS state (clean, stable or active): The FS state is used by the fsck utility when it is run during boot to determine what filesystems to check automatically. See more details on fsck in a future section.
Size of filesystem
Size of data blocks on filesystem
Size of the group blocks on this filesystem
Number of data blocks in filesystem
Path name of last mount point
Date and time of last update to the superblock
Typically this data is never updated or accessed by the system administrator. Knowing the contents of the superblock, however, can make understanding the functionality of the filesystem easier
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