VERITAS File System 4.1 Administrator's Guide

VxFS Performance: Creating, Mounting, and Tuning File Systems
Choosing mount Command Options
Chapter 240
Choosing mount Command Options
In addition to the standard mount mode(delaylog mode), VxFS provides blkclear, log,
tmplog, and nodatainlog modes of operation. Caching behavior can be altered with the
mincache option, and the behavior of O_SYNC and D_SYNC (see the fcntl (2) manual page)
writes can be altered with the convosync option.
The delaylog and tmplog modes can significantly improve performance. The improvement
over log mode is typically about 15 to 20 percent with delaylog; with tmplog, the
improvement is even higher. Performance improvement varies, depending on the operations
being performed and the workload. Read/write intensive loads should show less improvement,
while file system structure intensive loads (such as mkdir, create, and rename) may show
over 100 percent improvement. The best way to select a mode is to test representative system
loads against the logging modes and compare the performance results.
Most of the modes can be used in combination. For example, a desktop machine might use
both the blkclear and mincache=closesync modes.
Additional information on mount options can be found in the mount_vxfs (1M) manual page.
In the following descriptions, the term "effects of system calls" refers to changes to file system
data and metadata caused by the system call, excluding changes to st_atime (see the stat(2)
manual page).
log
In log mode, all system calls other than write(2), writev(2), and pwrite(2) are guaranteed
to be persistent once the system call returns to the application.
The rename(2) system call flushes the source file to disk to guarantee the persistence of the
file data before renaming it. In both modes, the rename is also guaranteed to be persistent
when the system call returns. This benefits shell scripts and programs that try to update a file
atomically by writing the new file contents to a temporary file and then renaming it on top of
the target file.
delaylog
The default logging mode is delaylog.Indelaylog mode, some system calls return before the
intent log is written. This logging delay improves the performance of the system, but some
changes are not guaranteed until a short time after the system call returns, when the intent