HP JFS 3.3 and HP OnLineJFS 3.3 VERITAS File System 3.3 System Administrator's Guide

64 Chapter2
Disk Layout
The VxFS Version 2 Disk Layout
Inode Allocation Unit
An Inode Allocation Unit (IAU) contains inode allocation information for
a given fileset. Each fileset contains one or more IAUs, each of which
details allocation for a set number of inodes. The number of inodes per
IAU varies, depending on the block size being used. One IAU exists for
every 16,384 inodes in a fileset with the default block size (1024 bytes). If
an IAU is damaged, the information that it contains can bereconstructed
by examining the fileset’s inode list.
The IAUs for a fileset are stored in sequential order in the fileset’s IAU
file. The fileset header identifies the attribute fileset inode associated
with that fileset’s IAU file.
Figure 2-8, “Inode Allocation Unit (IAU) Structure” shows the inode
allocation unit structure. All IAU components begin on a block boundary.
Figure 2-8 Inode Allocation Unit (IAU) Structure
IAU Header The IAU header verifies that the inode allocation unit
matches the fileset. The IAU header occupies the first block of each inode
allocation unit. If damaged, the IAU can be reconstructed from inodes
and other information.
IAU Summary The IAU summary summarizes the resources used in
the IAU. It includes information on the number of free inodes in the IAU
and the number of inodes with extended operation sets in the IAU. The
IAU summary is 1 block long.
Free Inode Map The free inode map is a bitmap that indicates which
inodes are free and which are allocated. A free inode is indicated by the
IAU Header
IAU Summary
Free Inode Map
Extended Inode Operations Map