HP-UX Reference (11i v1 00/12) - 1M System Administration Commands N-Z (vol 4)

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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man1m/naaagt.1m
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t
tunefs(1M) tunefs(1M)
NAME
tunefs - tune up an existing HFS file system
SYNOPSIS
/usr/sbin/tunefs [-A][-v][-a maxcontig ][-d rotdelay ][-e maxbpg][-m minfree ]
[-r advanced read-ahead] special-device
DESCRIPTION
The tunefs command is used to alter dynamic parameters that affect HFS file system layout policies.
Parameters to be altered are specified by the options and arguments provided on the command line as
described below.
tunefs affects how the file system blocks are laid out on the disk. The default rotdelay value set by the
newfs and mkfs commands (see newfs(1M) and mkfs(1M)) is 0 milliseconds, causing file system blocks to
be written and read consecutively. In general, this should be the optimal tuning, making the use of
tunefs -d unnecessary.
Options
tunefs recognizes the following options and command-line arguments:
-a maxcontig Set the maximum number of contiguous blocks that will be laid out before forcing a
rotational delay to maxcontig (see -d below). The default value is 1, because most
device drivers require one interrupt per disk transfer. For device drivers that can
chain several buffers together in a single transfer, set maxcontig to the maximum
chain length.
-d rotdelay rotdelay is the expected time (in milliseconds) to service a transfer completion inter-
rupt and initiate a new transfer on the same disk. It is used to determine how much
rotational spacing to place between successive blocks in a file.
-e maxbpg maxbpg specifies the maximum number of blocks any single file can allocate out of a
cylinder group before it is forced to begin allocating blocks from another cylinder
group. Typically this value is set to about one fourth of the total blocks in a cylinder
group. The intent is to prevent any single file from using up all the blocks in a single
cylinder group, thus degrading access times for all files subsequently allocated in that
cylinder group. The effect of this limit is to cause large files to do long seeks more fre-
quently than if they were allowed to allocate all the blocks in a cylinder group before
seeking elsewhere. For file systems with exclusively large files, this parameter should
be set higher.
-m minfree minfree specifies the percentage of space that is not available to normal users; i.e., the
minimum free space threshold. The default value used is 10%. This value can be set
to zero. If set to zero, throughput performance drops to as little as one-third of the
efficiency expected when the threshold is set at 10%. Note that if minfree is raised
above the current usage level, users cannot allocate files until enough files have been
deleted to meet the new threshold requirement.
-r advanced read-ahead
Advanced read-ahead specifies whether the file system should use an advanced predic-
tive read-ahead algorithm. The implementation requires more system resources in
exchange for an advanced access pattern recognition. Patterns include forward
sequential, backward sequential, forward strided, and backward strided. This value
can be set to zero (disable) or one (enable). By default, a file system will have
advanced read-ahead enabled when created.
-v (visual) Display current values contained in the primary super-block to standard out-
put.
-A (all) Modify redundant super-blocks as well as the primary super-block as stipulated
by the configuration options and arguments.
special-device is the name of the file system to be tuned. It is either a block or character special file
if the file system is not mounted, or a block special file if the file system is mounted.
WARNINGS
Root file system tuning is normally done during initial system software installation. Tuning the root file
system after installationhas little useful effect because so many files have already been written.
HP-UX Release 11i: December 2000 − 1 − Section 1M−−971
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