VERITAS File System 4.1 Administrator's Guide

VxFS Performance: Creating, Mounting, and Tuning File Systems

Kernel Tunables

Chapter 252

Changing the value of a tunable does not resize the internal hash tables and structures of the

caches. These sizes are determined at system boot up based on either the system memory size,

which is the default, or the value of the tunable if explicitly set, whichever is larger. Thus,

dynamically increasing the tunable to a value that is more than two times either the default

value or the user-deﬁned value, if larger, may cause performance degradation unless the

system is rebooted.

Examples of Changing the vx_inode Tunable Value

The following are examples of changing the vx_ninode tunable value.

Example 1 - Reporting the Current Value of vx_ninode

# kctune vx_ninode

This command displays the current value of vx_ninode.

Example 2 - Setting vx_ninode

# kctune -s vx_ninode=10000

This command sets vx_ninode to 10000, the speciﬁed value.

Example 3 - Restoring vx_ninode to Its Default Value

# kctune -s vx_ninode=

This command restores vx_ninode to its default value by clearing the user-speciﬁed value.

The default value is the value determined by VxFS to be optimal based on the amount of

system memory, which is used if vx_ninode is not explicitly set.

Example 4 - Delaying a Change to vx_ninode Until After a Reboot

# kctune -h -s vx_ninode=10000

If the -h option is speciﬁed, the speciﬁed value for vx_ninode will not take effect until after a

system reboot.

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.