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 tunefs(1M)							  tunefs(1M)

      tunefs - tune up an existing HFS file system

      /usr/sbin/tunefs [-A] [-v] [-a maxcontig] [-d rotdelay]
	   [-e maxbpg] [-m minfree]
	   [-r advanced read-ahead] special-device

      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

      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.

      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 interrupt 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 frequently
			  than if they were allowed to allocate all the
			  blocks in a cylinder group before seeking

 Hewlett-Packard Company	    - 1 -   HP-UX Release 11i: November 2000

 tunefs(1M)							  tunefs(1M)

			  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 predictive 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 output.

	   -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.

      Root file system tuning is normally done during initial system
      software installation.  Tuning the root file system after installation
      has little useful effect because so many files have already been

      You can tune a file system, but you can't tune a fish.

      tunefs was developed by the University of California, Berkeley.

      dumpfs(1M), mkfs(1M), newfs(1M), fs(4).

 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000

 tunefs(1M)							  tunefs(1M)

 Hewlett-Packard Company	    - 3 -   HP-UX Release 11i: November 2000