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tunefs(8)							    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

OPTIONS

  -a maxcontig
      Specifies	the maximum number of contiguous blocks	that will be laid out
      before forcing a rotational delay	(see the -d option).  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 succes-
      sive 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 the previous	list item) 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 a	problem, and the file system can be
      optimized	for time.





OPERANDS

  file_system
	  Specifies the	UFS file system	that is	being tuned.

DESCRIPTION

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

  You should unmount a file system before running the tunefs program. The
  tunefs program does allow you	to enter parameters for	a mounted and active
  file system.	However, your changes will not take effect until the file
  system is unmounted and mounted again	(or until after	the system is
  rebooted). If	you use	tunefs to tune the root	file system (assuming root is
  a UFS	file system), you must always reboot the system	in order for your
  changes to take effect.

  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.

  After	you specify an optimization preference,	it comes into play only	under
  the following	conditions:

    +  A file is growing

    +  It is not possible to extend a fragment

    +  There is	a choice between allocating an exact-sized fragment or allo-
       cating a	full block and freeing the unused portion of the block

  After	you specify an optimization preference,	the system first tries the
  specified preference when it reaches the minimum reserved space specified
  by the minfree value.	If you specified -o space, the system tries space
  optimization,	but switches to	time optimization if the file continues	to
  grow and fragmentation is less than half of the minimum free reserve.	If
  you specifed -o time,	the system tries time optimization, but	switches to
  space	optimization if	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.

SEE ALSO

  Commands: newfs(8)