HP-UX 11i Version 2 Installation and Update Guide, September 2004

Controlling Memory Utilization of VxFS 3.5 on HP-UX 11i v2
Introduction
Appendix C168
Introduction
VxFS 3.5 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 3.5 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.