Veritas 4.1 Installation Guide (HP-UX 11i v3, February 2007)

The various VxFS on-disk structures are:
• Superblock
Superblock (SB) resides ~8k from the beginning of the storage and tracks the status of the
file system. Supports maps of free space and other resources (inodes, allocation units, and
so on).
• Intent Log
VxFS reduces system failure recovery time by tracking file system activity in the VxFS intent
log. This feature records pending changes to the file system structure in a circular intent log.
The intent log recovery feature is not readily apparent to users or a system administrator
except during a system failure. During system failure recovery, the VxFS fsck utility
performs an intent log replay, which scans the intent log and nullifies or completes file
system operations that were active when the system failed. The file system can then be
mounted without completing a full structural check of the entire file system. Replaying the
intent log may not completely recover the damaged file system structure if there was a disk
hardware failure. Hardware problems may require a complete system check using the fsck
utility provided with VxFS.
• Allocation Unit
Allocation units are made up of series of data blocks. Each allocation unit typically consist
of 32k contiguos blocks. Contiguous data blocks make up an extent. The extents are used
for file data storage.
Extent Based Allocation
An extent is defined as one or more adjacent blocks of data within the file system. Extent based
allocation offers the following advantages:
• Allows large I/Os for efficiency.
• Dynamic resizing of disk space.
Supported File and File System Size
See "Supported File and File System Sizes”, white paper available at http://docs.hp.com for more
information on max file system and file sizes supported by VxFS.
20 Product Overview