System Administration Guide: Devices and File Systems


An inode contains all the information about a file except its name, which is kept in a directory. An inode is 128 bytes. The inode information is kept in the cylinder information block, and contains the following:

The array of 15 disk-block addresses (0 to 14) points to the data blocks that store the contents of the file. The first 12 are direct addresses. That is, they point directly to the first 12 logical storage blocks of the file contents. If the file is larger than 12 logical blocks, the 13th address points to an indirect block, which contains direct-block addresses instead of file contents. The 14th address points to a double indirect block, which contains addresses of indirect blocks. The 15th address is for triple indirect addresses. The following figure shows this chaining of address blocks starting from the inode.

Figure 23–1 Address Chain for a UFS File System

Graphic of relationship between the address array of
a UFS inode and the indirect and double indirect pointers to a file's storage