VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 2

VxFS Performance: Creating, Mounting, and Tuning File Systems

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 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:

vx_ninode 1000000

sets the inode table size to 1,000,000 inodes after making a new HP-UX kernel using mk_kernel and then

rebooting. You can also set the value using the sam or kmtune commands (see the sam (1M) and kmtune (1M)

manual pages)

VxFS Buffer Cache High Water Mark

VxFS maintains its own buffer cache in the kernel for frequently accessed file system metadata. This cache is

different from the HP-UX kernel buffer cache that caches file data. The vx_bc_bufhwm global tunable

parameter lets you change the VxFS buffer cache high water mark, that is, the maximum amount of memory

that can be used to cache VxFS metadata.

The initial value of vx_bc_bufhwm is zero. When the operating system reboots, VxFS sets the value of

vx_bc_bufhwm based on the amount of system memory. You can explicitly reset the value using the sam or

kmtune commands (see the the sam (1M) and kmtune (1M) manual pages). The change will take affect only

after a system reboot. You can also set the value by adding an entry to the system configuration file. For

example, the following entry:

vx_bc_bufhwm 300000

sets the high water mark to 300 megabytes. The change takes affect after you rebuild the HP-UX kernel using

the mk_kernel command and then rebooting the system. You specify the vx_bc_bufhwm tunable in units of

kilobytes. The minimum value is 6144.

Typically, the default value computed by VxFS based on the amount of system memory ensures good system

performance across a wide range of applications. For application loads that cause frequent file system

metadata changes on the system (for example, a high rate of file creation or deletion, or accessing large

directories), changing the value of vx_bc_bufhwm may improve performance.

You can use the vxfsstat command to monitor buffer cache statistics and inode cache usage (see the vxfsstat

(1M) manual page).