VERITAS File System 3.5 (HP OnlineJFS/JFS 3.5) Administrator's Guide (August 2003)

Chapter 2
VxFS Performance: Creating, Mounting, and Tuning File Systems
Choosing mount Command Options
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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.
log
With log mode, VxFS guarantees that all structural changes to the file system have been logged on disk when
the system call returns. If a system failure occurs, fsck replays recent changes so that they will not be lost.
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.
tmplog
In tmplog mode, intent logging is almost always delayed. This greatly improves performance, but recent
changes may disappear if the system crashes. This mode is only recommended for temporary file systems.
Fast file system recovery works with this mode.
logiosize
The logiosize=size option is provided to enhance the performance of storage devices that employ a
read-modify-write feature. If you specify logiosize when you mount a file system, VxFS writes the intent log
in at least size bytes to obtain the maximum performance from such devices. The values for size can be
1024, 2048, or 4096.