HP-UX 11i v3 Installation and Update Guide, September 2007 (Update 1 Release)

Introduction
VxFS 4.1 caches objects in memory to improve performance. Most of the memory
consumed by VxFS is used to cache inodes (in the inode cache) and metadata (in the
buffer cache). The sizes of these caches and the behavior of VxFS are controlled by a
set of tunables. You can tailor the performance of VxFS to meet a variety of usage
scenarios while taking into account variations in machine configurations via the use of
these tunables.
The default settings of these tunables are meant to provide good performance for typical
deployment configurations. However, these default values can result in the VxFS driver
consuming more memory, especially when the file systems are under heavy file system
load. For machines low on RAM, these tunables may need to be manually turned down
depending on the expected use of the machine and the performance required of the
file system.
VxFS 4.1 exposes two global tunables, vx_ninode and vxfs_bc_bufhwm, that control
the size of the inode cache and buffer cache, respectively, and thereby affect system
memory consumption by the file system driver.
This appendix discusses when and why the sizes of the inode and buffer caches need
to be tuned down from their default values in certain configurations. The following
sections describe these tunables in detail as well as the effects of changing their default
values.
132 Controlling Memory Utilization of VxFS 4.1