HP-UX 11i Version 1 Installation and Update Guide, June 2004

Controlling Memory Utilization of VxFS 3.5 on HP-UX 11i v1
Introduction
Appendix E214
Introduction
VxFS 3.5 resorts to caching objects in memory as a way 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 a
tunables. The performance of VxFS can be tailored to meet a variety of
usage scenarios 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 stressed (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 will need to be tuned down from their default values on certain
configurations. The following sections describe these tunables in detail
as well as the effects of changing their default values.