tunefs(1M)                    UNIX System V(UFS)                     tunefs(1M)


NAME
      tunefs - tune up an existing file system

SYNOPSIS
      tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree] [-o [s |
      space | t | time]] special | filesystem

DESCRIPTION
      tunefs is designed to change the dynamic parameters of a file system
      which affect the layout policies.  The file system must be unmounted
      before using tunefs.  The parameters which are to be changed are
      indicated by the options given below:

      The options are:

     -a maxcontig
              Specify the maximum number of contiguous blocks that will be laid
              out before forcing a rotational delay (see -d below).  The
              default value is one, since most device drivers require an
              interrupt per disk transfer.  Device drivers that can chain
              several buffers together in a single transfer should set this to
              the maximum chain length.

     -d rotdelay
              Specify 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
              Indicate 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 approximately 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
              Specify 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:  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.



10/89                                                                    Page 1

tunefs(1M)                    UNIX System V(UFS)                     tunefs(1M)


     -o [s | space | t | time]
              Change optimization strategy for the file system.  s and space
              are interchangeable, and t and time are interchangeable.
              s or space - conserve space.
              t or time - attempt to organize file layout to minimize access
              time.

      Generally one should optimize for time unless the file system is over 90%
      full.

SEE ALSO
      mkfs(1M)










































Page 2                                                                    10/89