VERITAS File System 4.1 Administrator's Guide

The VERITAS File System
Extent Attributes
Chapter 120
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 69, “Application Interface” on page 75, 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 37 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.