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

Chapter 1
The VERITAS File System
Extent Attributes
21
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 49, “Application
Interface” on page 55, and the setext (1)and getext (1) 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 29 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 provides recovery only seconds after a system failure by utilizing a tracking feature called intent
logging. This feature records pending changes to the file system structure in a circular intent log. 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. The intent log
recovery feature is not readily apparent to the user or the system administrator except during a system
failure.
Replaying the intent log may not completely recover the damaged file system structure if the disk suffers
a hardware failure; such situations may require a complete system check using the fsck utility provided
with VxFS.