The first 8 kbytes in each section is ignored, except where it coincides with the volume header discussed above. Each cylinder group has inodes and data. A file system is described by its super-block, which in turn describes the cylinder groups. The super-block is critical data and is replicated in each cylinder group to protect against catastrophic loss. This is done at file system creation time and the critical super-block data does not change, so the copies need not be referenced further unless disaster strikes.
Large files consist of exclusively large data blocks.
To avoid undue wasted disk space, the last data block of a file is allocated only as many fragments of a large block as are necessary, if that file is small enough to not require indirect data blocks. The file system format retains only a single pointer to such a fragment, which is a piece of a single large block that has been divided. I-numbers begin at 0. Inodes 0 and 1 are reserved. Inode 2 is used for the root directory of the file system.