Index for Section 8

Alphabetical listing for T

Bottom of page

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
      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 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
       allocating 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)

Index for Section 8

Alphabetical listing for T

Top of page