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

VxFS Performance: Creating, Mounting, and Tuning File Systems
Choosing mount Command Options
Chapter 228
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. In delaylog 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 log is written. If a system failure occurs,
recent changes may be lost. This mode approximates traditional UNIX guarantees for correctness in case of
system failures. Fast file system recovery works with this mode.