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.