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tunefs(8)
NAME
  tunefs - Tunes an existing UFS file system

SYNOPSIS
  /usr/sbin/tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree] [-o
       optimization_preference] file_system

FLAGS
  -a maxcontig
	    Specifies the maximum number of contiguous blocks that will be
	    laid out before forcing a rotational delay (see the -d flag).
	    The default value is 8.  Device drivers that can chain several
	    buffers together in a single transfer should set this to the
	    maximum chain length.

  -d rotdelay
	    Specifies the expected time (in milliseconds) to service a
	    transfer completion interrupt and initiate a new transfer on the
	    same disk.	It is used to decide how much rotational spacing to
	    place between successive blocks in a file.

  -e maxbpg Indicates 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, you
	    set this value to about one quarter 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 big
	    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.

  -m minfree
	    Specifies the percentage of space held back from normal users;
	    the minimum free space threshold.  The default value used is 10%.
	    This value can be set to zero, however up to a factor of three in
	    throughput will be lost over the performance obtained at a 10%
	    threshold.	Note that if the value is raised above the current
	    usage level, users will be unable to allocate files until enough
	    files have been deleted to get under the higher threshold.

  -o optimization_preference
	    Specifies whether the file system should try to minimize the time
	    spent allocating blocks (-o time) or try to minimize the space
	    fragmentation on the disk (-o space).  If the value of minfree
	    (see above) is less than 10%, then the file system should
	    optimize for space to avoid running out of full sized blocks.
	    For values of minfree greater than or equal to 10%, fragmentation
	    is unlikely to be problematical, and the file system can be
	    optimized for time.




DESCRIPTION
  The tunefs command changes the dynamic parameters of a UFS file system
  which affect the layout policies.  The parameters which are to be changed
  are indicated by the flags specified.

  This program should work on mounted and active file systems.	Because the
  superblock is not kept in the buffer cache, the changes will only take
  effect if the program is run on unmounted file systems.

  The system must be rebooted after the root file system is tuned.

  For larger-capacity devices, set minfree to five percent.

  The rotdelay value is useful for disks that do not have read-ahead cache,
  such as the RA-series disks.	For disks that have read-ahead cache, set
  rotdelay to zero.

  When you specifiy an optimization preference, it only comes into play in
  the following circumstances:	when a file is growing; when it is not
  possible to extend a fragment; and when there is a choice between the
  following paths:

      Allocating an exact-sized fragment

      Allocating a full block and freeing the unused portion of the block
      When you specify an optimization preference, the system will first try
      that method when it reaches the minimum reserved space specified in
      minfree.	If you specify space optimization, the system will try that,
      but switch to time optimization when the file continues to grow and
      fragmentation is less than half of the minimum free reserve.  If you
      specify time optimization, the system will try that, but switch to
      space optimization when the file growth causes disk fragmentation to
      reach within two percent of the minimum free reserve.

  You must be the root user to use this command.

FILES
  /usr/sbin/tunefs
	    Specifies the command path

RELATED INFORMATION
  Commands:  newfs(8)

Index for Section 8

Alphabetical listing for T

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