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

70 Chapter2
Disk Layout
The VxFS Version 3 Disk Layout
allocated.
extent allocation unit summary file Contains the AU summary for each
allocation unit, which contains the
number of free extents of each size.
The summary for an extent is created
only when an allocation unit is
expanded for use.
free extent map file Contains the free extent maps for
each of the allocation units.
quotas file If the file system supports quotas,
there is a quotas file which is used to
track the resources allocated to each
user.
Figure 2-10, “VxFS Version 3 Disk Layout” shows how the kernel and
utilities build information about the structure of the file system. The
super-block location is in a known location from which the OLT can be
located. From the OLT, the initial extents of the structural inode list can
be located along with the inode number of the fileset header file. The
initial inode list extents contain the inode for the fileset header file from
which the extents associated with the fileset header file are obtained.
As an example, when mounting the file system, the kernel needs to
access the primary fileset in order to access its inode list, inode allocation
unit, quotas file and so on. The required information is obtained by
accessing the fileset header file from which the kernel can locate the
appropriate entry in the file and access the required information.