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vxfs_bc_bufhwm - VxFS buffer cache high water mark, which determines the VxFS buffer cache size


/usr/sbin/kctune -s vxfs_bc_bufhwm=max_buffer_cache_size


Specify an integer value, in kilobytes.
Minimum 6144
Maximum 90% of kernel memory
Default 0


VxFS maintains a buffer cache in the kernel for frequently accessed file system metadata in addition to the HP-UX kernel buffer cache that caches the file data. The vxfs_bc_bufhwm tunable parameter determines the size of the VxFS buffer cache, which is the maximum amount of memory that can be used to cache VxFS metadata.

The default value computed based on the amount of system memory ensures good system performance across a wide range of applications.

The value of vxfs_bc_bufhwm is specified in kilobytes. To improve performance during application loads that cause frequent file system metadata changes on the system, such as a high rate of file creation or deletion, or accessing large directories, change the value of vxfs_bc_bufhwm.


Use the vxfsstat command to monitor buffer cache statistics and inode cache usage. See the vxfsstat(1M) manual page.

Setting the vxfs_bc_bufhwm value too low can result in a system hang. Set the value of vxfs_bc_bufhwm to 5% or more of the system’s total physical memory if the system has 8 GB or less physical memory. Set the value of vxfs_bc_bufhwm to 2% or more of the system’s total physical memory if the system has more than 8 GB of physical memory. The higher the physical memory of the system, the lower you can set vxfs_bc_bufhwm. You can set vxfs_bc_bufhwm to as low as 0.5% of the system’s total physical memory if the system has much more than 8 GB of memory.


The following command sets the maximum of size of buffer cache at 300000:

# kctune -s vxfs_bc_bufhwm=300000


Incorrectly tunning a parameter may adversely affect system performance. See the Storage Foundation Administrator’s Guide for more information about tuning parameters.

VxFS kernel tunable parameters are release specific. This parameter may be removed or the default value and usage may change in future releases. See the Storage Foundation Release Notes for information about changes to parameters, if any.


kctune(1M), vxfsstat(1M), vx_maxlink(5), vx_ninode(5), vxfs_ifree_timelag(5)

Storage Foundation Administrator’s Guide

VxFS 7.4 vxfs_bc_bufhwm(5)