VERITAS File System 4.1 Administrator's Guide

Disk Layout
Disk Layout
Appendix C254
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 files There is a quotas file which is used to track the resources allocated to each
user and a quotas.grp file to track the resources allocated to each group.
The following figure 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.
The Version 4 disk layout supports Access Control Lists and Block-Level Incremental (BLI)
Backup. BLI Backup is a backup method that stores and retrieves only the datablocks
changed since the previous backup, not entire files. This saves times, storage space, and
computing resources required to backup large databases. This file system technology is
implemented in other VERITAS products. For information on how to use this feature, contact
your sales channel.