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

Chapter 5 105
Performance and Tuning
I/O Tuning
I/O Tuning
NOTE The tuneables and the techniques described in this section are for tuning
on a per file system basis and should be used judiciously based on the
underlying device properties and characteristics of the applications that
use the file system.
Performance of a file system can be enhanced by a suitable choice of I/O
sizes and proper alignment of the I/O requests based on the
requirements of the underlying special device. VxFS provides tools to
tune the file systems.
Tuning VxFS I/O Parameters
The VxFS file system provides a set of tuneable I/O parameters that
control some of its behavior.
If the default parameters are not acceptable, then the
/etc/vx/tunefstab file can be used to set values for I/O parameters.
The mount_vxfs(1M) command invokes the vxtunefs(1M) command to
process the contents of the /etc/vx/tunefstab file. Please note that the
mount command will continue even if the call to vxtunefs fails or if
vxtunefs detects invalid parameters. While the file system is mounted,
any I/O parameters can be changed using the vxtunefs command which
can have tuneables specified on the command line or can read them from
the /etc/vx/tunefstab file. For more details, see vxtunefs(1M) and
tunefstab(4). The vxtunefs command can be used to print the current
values of the I/O parameters.
Tuneable VxFS I/O Parameters
read_pref_io The preferred read request size. The file system uses this in conjunction
with the read_nstream value to determine how much data to read
ahead. The default value is 64K.
write_pref_io The preferred write request size. The file system uses this in conjunction
with the write_nstream value to determine how to do flush behind
on writes. The default value is 64K.