HP JFS 3.3 and HP OnLineJFS 3.3 VERITAS File System 3.3 System Administrator's Guide

Chapter 5 95
Performance and Tuning
Choosing Mount Options
Choosing Mount Options
In addition to the standard mount mode (log mode), VxFS provides
blkclear, delaylog, tmplog, nolog, and nodatainlog modes of
operation. Caching behavior can be altered with the mincache option,
and the behavior of O_SYNC and D_SYNC (see fcntl(2)) writes can be
altered with the convosync option.
The delaylog and tmplog modes are capable of significantly improving
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
mount_vxfs(1M).
log
The default logging mode is 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
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.