Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

The VERITAS File System
Extent Attributes
Chapter 18
Extent Attributes
VxFS allocates disk space to files in groups of one or more extents. VxFS also allows applications to control
some aspects of the extent allocation. Extent attributes are the extent allocation policies associated with a
file.
The setext and getext commands allow the administrator to set or view extent attributes associated
with a file, as well as to preallocate space for a file. Refer to “Extent Attributes” on page 53, “Application
Interface” on page 59, and the setext (1M)and getext (1M) manual pages for discussions on how to use
extent attributes.
The vxtunefs command allows the administrator to set or view the default indirect data extent size. Refer
to “VxFS Performance: Creating, Mounting, and Tuning File Systems” on page 25 and the vxtunefs (1M)
manual page for discussions on how to use the indirect data extent size feature.
Fast File System Recovery
Most file systems rely on full structural verification by the fsck utility as the only means to recover from a
system failure. For large disk configurations, this involves a time-consuming process of checking the entire
structure, verifying that the file system is intact, and correcting any inconsistencies.
VxFS Intent Log
VxFS reduces system failure recovery times 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.
Intent Log Resizing
The VxFS intent log is allocated when the file system is first created. The size of the intent log is based on
the size of the file system-the larger the file system, the larger the intent log. The maximum default intent
log size of disk layout Versions 4, 5 and 6 is 16 megabytes.