VERITAS File System 4.1 Administrator's Guide

The VERITAS File System
Extended mount Options
Chapter 1 25
Using the log Option for Data Integrity
File systems are typically asynchronous in that structural changes to the file system are not
immediately written to disk, which provides better performance. However, recent changes
made to a system can be lost if a system failure occurs. Specifically, attribute changes to files
and recently created files may disappear.
The mount -o log intent logging option guarantees that all structural changes to the file
system are logged to disk before the system call returns to the application.With this option,
the rename(2) system call flushes the source file to disk to guarantee the persistent of the file
data before renaming it. The rename() call is also guaranteed to be persistent when the
system call returns. The changes to file system data and metadata caused by the fsync(2)
and fdatasync(2) system calls are guaranteed to be persistent once the calls return.
Enhanced Performance Mode
VxFS has several mount options that improve performance such as delaylog.
Using the delaylog Option for Enhanced Performance
The default VxFS logging mode, mount -o delaylog, increases performance by delaying the
logging of some structural changes, but does not provide the equivalent data integrity as the
previously described modes. That is because recent changes may be lost during a system
failure. This option provides at least the same level of data accuracy that traditional UNIX
file systems provide for system failures, along with fast file system recovery. delaylog is the
default mount option.
Modes of Temporary File System
On most UNIX systems, temporary file system directories (such as /tmp and /usr/tmp) often
hold files that do not need to be retained when the system reboots. The underlying file system
does not need to maintain a high degree of structural integrity for these temporary
directories.
Using the tmplog option For Temporary File Systems
VxFS provides a mount -o tmplog option which allows the user to achieve higher
performance on temporary file systems by delaying the logging of most operations.
Improved Synchronous Writes
VxFS provides superior performance for synchronous write applications. The default mount
datainlog option greatly improves the performance of small synchronous writes.