Inodebased

Inodebased describes file systems whose core metadata model is centered on inodes, or index nodes. An inode is a structured record that stores a file’s attributes—type, permissions, ownership, timestamps, size—and pointers to the blocks that hold the file’s data. Inodebased file systems separate metadata from file content: a file is represented by an inode, while directories map file names to inode numbers.

Each file has a dedicated inode. Directory entries pair a file name with the inode number, enabling multiple directory entries to refer to the same inode (hard links). The inode’s data block pointers typically include direct pointers to data blocks, plus indirect pointers to blocks that contain additional pointers. Some modern implementations use extents or other mechanisms, but the inode remains the primary descriptor of a file’s identity.

Advantages of the inodebased approach include fast metadata access, stable file identification via inode numbers, and support for hard links. It also simplifies scaling to large numbers of files. Limitations include a fixed inode pool allocated at filesystem creation, which can limit the total number of files, and potential fragmentation or allocation overhead in metadata management.

Examples of inodebased file systems include Linux ext2, ext3, and ext4, and various UNIX-like systems such as UFS. While many modern systems incorporate enhancements (such as journaling or extents) that modify the classic inode layout, the inode-based model remains a common foundation for metadata management in traditional Unix-like file systems.

See also: inode, inode table, hard link, directory, ext4, UFS.