tunefs(1M)																tunefs(1M)

NAME

       tunefs - tune up an existing HFS file system

SYNOPSIS

       maxcontig] rotdelay] maxbpg] minfree]
	      advanced read-ahead] special-device

DESCRIPTION

       The 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.

       affects how the file system blocks are laid out on the disk.  The default rotdelay value  set  by  the  and  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 tun-
       ing, making the use of unnecessary.

   Options
       recognizes the following options and command-line arguments:

	      Set the maximum number of contiguous blocks that will be laid out
			     before forcing a rotational delay to maxcontig (see below).  The default value is 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.

	      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.

	      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 cylin-
			     der 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 elsewhere.  For file systems with exclusively large files,  this  parameter
			     should be set higher.

	      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.

	      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.

	      (visual) Display current values
			     contained in the primary super-block to standard output.

	      (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 installation has
       little useful effect because so many files have already been written.

AUTHOR

       was developed by the University of California, Berkeley.

SEE ALSO

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

																	tunefs(1M)