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Each Block Group has a data structure describing it.
Like the Superblock, all the group descriptors
for all of the Block Groups are duplicated in each Block Group in case of file system
Each Group Descriptor contains the following information:
The group descriptors are placed on after another and together they make the group
Each Blocks Group contains the entire table of group descriptors after its copy of
Only the first copy (in Block Group 0) is actually used by the EXT2 file system.
The other copies are there, like the copies of the Superblock, in case the main
copy is corrupted.
- Blocks Bitmap
- The block number of the block allocation bitmap for
this Block Group. This is used during block allocation and deallocation,
- Inode Bitmap
- The block number of the inode allocation bitmap for
this Block Group. This is used during inode allocation and deallocation,
- Inode Table
- The block number of the starting block for the inode table for
this Block Group. Each inode is represented by the EXT2 inode data structure
- Free blocks count, Free Inodes count, Used directory count
David A. Rusling