HP-UX 11i Version 1 Installation and Update Guide, June 2004
Controlling Memory Utilization of VxFS 3.5 on HP-UX 11i v1
Controlling the Buffer Cache
Appendix E216
Controlling the Buffer Cache
VxFS 3.5 implements a private buffer cache used exclusively for
metadata. The allocations made for this buffer cache are not static but
grow and shrink during system usage depending on the load on the file
system. The global (static) tunable, vxfs_bc_bufhwm, represents the
maximum possible size of the VxFS buffer cache. The maximum size of
the metadata buffer cache is decided (auto-tuned) at boot time based on
system memory size, provided that the value of vxfs_bc_bufhwm is set to
zero (default).
As with the tunable vx_ninode, a large metadata buffer cache can help
improve file system performance especially during metadata-intensive
loads (stat, create, remove, link, lookup operations). However, systems
low on RAM (having typically 1GB/CPU or less) may not need a large
metadata buffer cache if file system load is not metadata-intensive or
performance is not critical. In such circumstances, the value of
vxfs_bc_bufhwm can be manually tuned down, subject to a minimum of
6144 (6MB).