fs_async.5 (2010 09)

fs_async(5) fs_async(5)

(Tunable Kernel Parameters)

If fs_async is set to allow asynchronous writes and a crash occurs,

fsck does not know what sequence

was used, and thus will probably require interactive assistance from the administrator while ﬁxing incon-

sistent ﬁle system information, repairing directory and inode entries, and so on.

Why Allow Asynchronous Writes?

Waiting for synchronous writing and updating of disk blocks when closing ﬁles after writing to them

degrades the performance of programs and applications that require frequent ﬁle and directory write and

close operations. Allowing asynchronous writing signiﬁcantly reduces those delays, producing a

corresponding improvement in performance. However, when applications are CPU intensive with rela-

tively little disk I/O, performance improvements are much lower.

When Should I Use Asynchronous Writes?

Asynchronous writing is advisable for improving system performance if:

• Risk of power failure is low (very dependable power source and/or uninterruptible power

sources).

• Precautions have been taken to enhance data security (sophisticated ﬁle system backup or

redundancy strategies), or potential loss of data due to a system crash is less important than sys-

tem performance.

• User applications require frequent opening, writing, and closing of disk ﬁles and directories.

• Elimination of synchronous writing would improve system performance sufﬁciently to offset any

associated risks.

To enable asynchronous writing, set the

fs_async kernel parameter to 1 instead of the default value of

WARNINGS

All HP-UX kernel tunable parameters are release speciﬁc. This parameter may be removed or have its

meaning changed in future releases of HP-UX.

Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-

ter values. After installation, some tunable parameters may no longer be at the default or recommended

values. For information about the effects of installation on tunable values, consult the documentation for

the kernel software being installed. For information about optional kernel software that was factory

installed on your system, see HP-UX Release Notes at http://www.hp.com/go/hpux-core-docs

AUTHOR

fs_async was developed by HP.