VERITAS File System 4.1 Administrator's Guide

VxFS Performance: Creating, Mounting, and Tuning File Systems
Kernel Tunables
Chapter 2 51
Kernel Tunables
This section describes the kernel tunable parameters in VxFS.
Internal Inode Table Size
VxFS caches inodes in an inode table. There is a dynamic tunable in VxFS called vx_ninode
that determines the number of entries in the inode table.
A VxFS file system obtains the value of vx_ninode from the system configuration file used for
making the HP-UX kernel (/stand/system for example). This value is used to determine the
number of entries in the VxFS inode table. By default, vx_ninode initializes at zero; the file
system then computes a value based on the system memory size. To change the computed
value of vx_ninode, you can add an entry to the system configuration file. For example:
vxfs_inode_table vx_ninode1000000
sets the inode table size to 1,000,000 inodes after making a new HP-UX kernel using
mk_kernel. You can also change the value of vx_ninode by using the sam or kctune
commands (see the sam(1M) and kctune(1M) manual pages).
Increasing the value of vx_ninode increases the inode table size immediately, allowing a
higher number of inodes to be cached. Decreasing the value of vx_ninode decreases the inode
table size to the specified value. After the tunable is decreased, VxFS attempts to free excess
cached objects so that the resulting number of inodes in the table is less than or equal to the
specified value of vx_ninode. If this attempt fails, the value of the vx_ninode tunable is not
changed. In such a case, the kctune command can be specified with the -h option so that the
new value of vx_ninode takes effect after a system reboot.
Be careful when changing the value of vx_ninode, as the value can affect file system
performance. Typically, the default value determined by VxFS based on the amount of system
memory ensures good system performance across a wide range of applications. However, if it
is determined that the default value is not suitable, vx_ninode can be set to an appropriate
value based on the expected file system usage. The vxfsstat command can be used to
monitor inode cache usage and statistics to determine the optimum value of vx_ninode for
the system.