Veritas™ File System 5.0.1 Administrator's Guide

■ The mount command 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.
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.
To print the values, type the following command:
# vxtunefs -p mount_point
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/metasave
read_pref_io=128k,write_pref_io=128k,read_nstream=4,write_nstream=4
/dev/vx/dsk/userdg/solbuild
read_pref_io=64k,write_pref_io=64k,read_nstream=4,write_nstream=4
/dev/vx/dsk/userdg/solrelease
read_pref_io=64k,write_pref_io=64k,read_nstream=4,write_nstream=4
/dev/vx/dsk/userdg/solpatch
read_pref_io=128k,write_pref_io=128k,read_nstream=4,write_nstream=4
Tunable I/O parameters
Table 2-1 provides a list and description of these parameters.
Table 2-1
Tunable VxFS I/O parameters
DescriptionParameter
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.
read_pref_io
VxFS performance: creating, mounting, and tuning file systems
Tuning I/O
52