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

VxFS Performance: Creating, Mounting, and Tuning File Systems
I/O Tuning
Chapter 2 43
I/O Tuning
NOTE The tunables and the techniques described in this section work on a per file system basis.
Use them 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
VxFS provides a set of tunable I/O parameters that control some of its behavior. These I/O parameters are
useful to help the file system adjust to striped or RAID-5 volumes that could yield performance superior to a
single disk. Typically, data streaming applications that access large files see the largest benefit from tuning
the file system.
If VxFS is being used with the VERITAS Volume Manager, the file system queries VxVM to determine the
geometry of the underlying volume and automatically sets the I/O parameters. The mount command also
queries VxVM when the file system is mounted and downloads the I/O parameters.
If the default parameters are not acceptable or the file system is being used without VxVM, then the
/etc/vx/tunefstab file can be used to set values for I/O parameters. The mount command reads the
/etc/vx/tunefstab file and downloads any parameters specified for a file system. The tunefstab file
overrides any values obtained from VxVM. While the file system is mounted, any I/O parameters can be
changed using the vxtunefs command which can have tunables specified on the command line or can read
them from the /etc/vx/tunefstab file. For more details, see the vxtunefs (1M) and tunefstab (4) manual
pages. The vxtunefs command can be used to print the current values of the I/O parameters:
# vxtunefs -p mount_point
If the default alignment from mkfs is not acceptable, the -o align=n option can be used to override
alignment information obtained from VxVM. The following is an example tunefstab file:
/dev/vx/dsk/userdg/netbackup
read_pref_io=128k,write_pref_io=128k,read_nstream=4,write_nstream=4
/dev/vx/dsk/userdg/opt
read_pref_io=128k,write_pref_io=128k,read_nstream=4,write_nstream=4
/dev/vx/dsk/userdg/metasave
read_pref_io=128k,write_pref_io=128k,read_nstream=4,write_nstream=4