Silicon Graphics IRIS Workstation User Manual page 52

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IRIS WORKSTATION GUIDE

of free inodes, and part of the free-inode list.

The super-block of a mounted file system (the root file system is always

mounted) is written to the file system whenever the file system is unmounted

or a sync command is issued.

Inodes

An inode contains information about the type of inode (directory, data, or

special), the number of directory entries linked to the inode, the list of blocks

claimed by the inode, and the size of the inode.

An inode is written to the file system upon closure

the inode.

Indirect Blocks

There are three types of indirect blocks: single-indirect, double-indirect and

triple-indirect. A single-indirect block contains a list of some of the block

numbers claimed by an inode. Each one of the 256 entries in an indirect block

is a data-block number. A double-indirect block contains a list of single-

indirect block numbers. A triple-indirect block contains a list of double-indirect

block numbers.

Indirect blocks are written to the file system whenever they have been

modified and released

Data Blocks

A data block may contain file information or directory entries. Each directory

entry consists of a file name and an inode number.

Data blocks are written to the file system whenever they have been modified

and released by the operating system.

First Free-List Block

The super-block contains the first free-list block. The free-list blocks are a list

of all blocks that are not allocated to the super-block, inodes, indirect blocks, or

data blocks. Each free-list block contains a count of the number of entries in

this free-list block, a pointer to the next free-list block, and a partial list of free

blocks in the file system.

1. All in core blocks are also written to the file system upon issue of a sync system call.

2. More precisely, they are queued for eventual writing. Physical I/O is deferred until the

buffer is needed by UNIX or a sync command is issued.

by the operating system.

of the file associated with

Appendix B:

Version 1.0

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