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

The VERITAS File System
Extended mount Options
Chapter 1 13
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.
The mount convosync=dsync option improves the performance of applications that require
synchronous data writes but not synchronous inode time updates.