VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 1
The VERITAS File System
Extent Attributes
7
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 37, “Application Interface”
on page 43, 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 17 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.
NOTE The use of QuickLog does not affect fast file system recovery.