VERITAS File System 3.5 (HP OnlineJFS/JFS 3.5) Administrator's Guide (August 2003)

Appendix C
Disk Layout
The VxFS Version 4 Disk Layout
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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 data blocks 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.
inode list file Both the primary fileset and the structural fileset have their own set of
inodes stored in an inode list file. Only the inodes in the primary fileset
are visible to users. When the number of inodes is increased, the kernel
increases the size of the inode list file.
inode allocation unit file Holds the free inode map, extended operations map, and a summary of
inode resources.
log file Maps the block used by the file system intent log.
extent allocation unit
state file
Indicates the allocation state of each AU by defining whether each AU is
free, allocated as a whole (no bitmaps allocated), or expanded, in which
case the bitmaps associated with each AU determine which extents are
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 files There is a quotas file which is used to track the resources allocated to
each user and a quotas.group file to track the resources allocated to each
group.