Next  Contents  Prev



The first block present on the block device is the boot block after that the ext2fs divides the disk up into groups with the first group on the disk holding the following data:-

The Super Block

File system descriptors

Block bit maps

Inode bit maps

Inode table

Data blocks

An important thing to note here is that the all the data structures are based on the block rather than the physical sector size. This goes way back to early days of Unix and abstraction of “block devices.”

The first revision of ext2 stores a copy of the super at the start of every block group. Later revisions store a copy in selected block groups to reduce the amount of redundancy on large filesystems. The groups chosen are 0, 1 and powers of 3, 5 and 7. Next on the disk is the group descriptor structure which holds information on where the other data structures are located for this group. These are at the start of each group or follow the super block when present.

The block bit maps and Inode bit maps are next.

Next is the actual Inodes and then the Data blocks.

At the end of these data blocks a new group starts.

The size of these structures is determined in the Super Block which is why its wise to have a copy.

Next  Contents  Prev