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

Controlling Memory Utilization of VxFS 3.5 on HP-UX 11i v2
Controlling the Buffer Cache
Appendix C170
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 set (auto-tuned) at
boot time based on system memory size, provided that the value of
vxfs_bc_bufhwm is set to zero (default).
Like 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).
Systems low on RAM (having typically 1GB/CPU or less) may not need a
large metadata buffer cache if the file system load is not
metadata-intensive or when performance is not critical. In such
circumstances, the value of vxfs_bc_bufhwm can be manually tuned
down, subject to a minimum of 6MB.