HP-UX 11i v3 Installation and Update Guide, September 2007 (Update 1 Release)

Controlling the inode Cache
As a matter of course, VxFS file systems allocate and free up inodes as required by the
load on the file system. VxFS caches these inodes for better performance (faster lookups).
In general, larger inode caches help file systems perform better for file server and web
server loads. The global (static) tunable vx_ninode represents the maximum possible
size of the VxFS inode cache.
Normally, the size of the inode cache is decided (auto-tuned) at boot time by VxFS
depending on the amount of physical memory in the machine, provided that the value
of vx_ninode is set to zero (default).
However, systems low on RAM (having typically 1.5 GB/CPU) may not require a large
inode cache if file systems are not exposed to file server and web server loads, or when
file system performance is not critical. HP recommends that you set a minimum value
as specified below based on the memory configuration.
VxFS inode Cache (number of inodes)Physical Memory or Kernel Available Memory
163841.5 GB
327682 GB
655363 GB
131072> 3 GB
NOTE: Default values are set at boot time and the values are not automatically adjusted
when memory is added, removed or migrated at run time.
Controlling the Buffer Cache
VxFS 4.1 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 1.5 GB/CPU) 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 6 MB.
Controlling the inode Cache 133