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).
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