%% File System Parameters
%%% Generic File System Parameters
% FDFLUSHR
Specifies the time interval, in seconds,
for checking the need to write
the buffer caches and file system pages to disk.
% FLCKREC
This parameter controls
the number of record locking structures used by
the system.
% NAUTOUP
Specifies the time, in seconds,
for automatic file system updates
(for both the buffer cache and file system pages).
A system buffer is written to the hard disk when it has
been memory-resident for the interval specified by the
NAUTOUP
parameter.
Specifying a smaller limit increases system reliability
(by writing the buffer caches and file system pages
to disk more frequently)
and decreases system performance.
Specifying a larger limit increases
system performance at the expense of reliability.
% NC_HASH_SIZE
Specifies the number of hash buckets
used for lookup in the DNLC.
The default value of 64 should be sufficient
unless the number of entries is increased dramatically.
% ROOTFSTYPE
Default root file system type.
% RSTCHOWN
Specifies restricted file ownership changes flag.
Only 0 and 1 are valid values for
RSTCHOWN.
A value of 0 is the Release 3 compatibility mode.
As in Release 3, the owner
of a file can change the user ID and group ID
of the file to any value,
including non-existent user IDs and group IDs.
When set to
1,
RSTCHOWN
specifies the FIPS/BSD compatibility mode.
This restricts the ability to change ownership of a file.
Only the user with appropriate privilege or
root processes (those whose UID is 0) can change
the ownership of a file.
The owner of the file
may change only the group ID of the file
to one group
in which the owner has membership.
[See
getgroups(2)].
A user with appropriate privilege and root processes
may change the group ID of any file to any value.
%%% Buffer Cache Parameters
% NBUF
Buffer cache
I/O
uses both buffers and buffer headers.
(See BUFHWM.)
Whenever a buffer header is needed,
but none is available,
the system dynamically allocates more buffer
headers in chunks of
NBUF
headers at a time.
There is no limit to the number of
buffer headers in the system, but the tunable
BUFHWM
limits the number of kilobytes
that may be used by buffers
and thus effectively limits
the number of buffer headers that will be allocated.

Once allocated, buffer header space cannot
be freed for other uses.
Therefore, take care when you raise
the value of
NBUF.
A higher value of
NBUF
decreases the number of times
the Kernel Memory Allocator
must be called to allocate space for buffer
headers, but this can result in the
allocation of headers that are not used.
% NHBUF
Specifies the size of the hash table
used to locate a buffer,
given a device number and a block number.
The value must be a power of 2 from 32 to 1024, inclusive.
This value should be about
one quarter of the total buffers available.
A value between 1/8 and 1/4 of
BUFHWM
is typically sufficient.
% NPBUF
Specifies the number of physical I/O buffers to allocate;
one is needed for each active physical read or write.
There is not a rule for adjusting
NPBUF .
However, if you expect a lot of I/O
and file system activity,
improvement may be gained by raising
NPBUF .
In test cases, raising
NPBUF
to 40 improved system performance.
% NPGOUTBUF
Specifies the number of buffer headers reserved for the
pageout daemon to avoid deadlock.
