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

VxFS Performance: Creating, Mounting, and Tuning File Systems
Kernel Tunables
Chapter 2 39
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 of
vx_bc_bufhwm by changing the value of vxfs_bc_bufhwm using the sam or kctune commands (see
the sam(1M) and kctune(1M) manual pages). You can also set the value by adding an entry to the system
configuration file. For example, the following entry:
vxfs_bc_bufhwm vx_bc_bufhwm 300000
sets the high water mark to 300 megabytes. The change takes effect after you rebuild the HP-UX kernel
using the mk_kernel command. You specify the vx_bc_bufhwm tunable in units of kilobytes. The
minimum value is 6144.
Increasing the value of vx_bc_bufhwm increases the VxFS buffer cache immediately, allowing a greater
amount of memory to be used to cache VxFS metadata. Decreasing the value of vx_bc_bufhwm decreases
the VxFS buffer cache to the specified value. This frees memory such that the amount of memory used for
buffer cache is lower than the specified value of vx_bc_bufhwm.
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).
Number of Links to a File
In VxFS, the number of possible links to a file is determined by the vx_maxlink global tunable. The
default value of vx_maxlink is 32767, the maximum value is 65535. This is a static tunable.
You can set the value of vx_maxlink using the sam or kctune commands (see the sam(1M) and
kctune(1M) manual pages), or by adding an entry to the system configuration file as shown in the following
example:
vxfs_maxlink vx_maxlink 40000
This sets the value of vx_maxlink to 40,000 links.
VxFS Inode Free Time Lag
In VxFS, an inode is put on a freelist if it is not being used. The memory space for this unused inode can be
freed it it stays on the freelist for a specified amount of time.
The vxfs_ifree_timelag tunable specifies the minimum amount of time an unused inode spends on a
freelist before its memory space is freed.vxfs_ifree_timelag is a dynamic tunable. Any changes to
vxfs_ifree_timelag take affect immediately.