The on-disk format of the UFS file system has largely remained unchanged with the introduction of new features, maintaining forward compatibility across all releases. This allows Solaris to be upgraded without the need to back up and restore file systems.
Information about which data blocks relate to each file are stored in a special file index node: the inode. The inode contains all of the information about the file, except for the file name, which is stored in the directory. Inode information includes:
File type (regular, special, fifo, link, etc.)
Owner of file (uid)
Group of file (gid)
Attributes (read, execute, modify)
Timestamps (last modified, etc.)
Number of references to the file (links) ...