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 vx_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 vx_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 the file system
load is not metadata-intensive or performance is not critical. In
such circumstances, the value of vx_bc_bufhwm can
be manually tuned down, subject to a minimum of 6144 (6MB).
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