tunefs(1M)                                                       tunefs(1M)




 NAME    [Toc]    [Back]
      tunefs - tune up an existing HFS file system

 SYNOPSIS    [Toc]    [Back]
      /usr/sbin/tunefs [-A] [-v] [-a maxcontig] [-d rotdelay]
           [-e maxbpg] [-m minfree]
           [-r advanced read-ahead] special-device

 DESCRIPTION    [Toc]    [Back]
      The tunefs 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.

      tunefs affects how the file system blocks are laid out on the disk.
      The default rotdelay value set by the newfs and mkfs commands (see
      newf
) is 0 milliseconds, causing file system blocks
      to be written and read consecutively.  In general, this should be the
      optimal tuning, making the use of tunefs -d unnecessary.

    Options    [Toc]    [Back]
      tunefs recognizes the following options and command-line arguments:

           -a maxcontig   Set the maximum number of contiguous blocks that
                          will be laid out before forcing a rotational delay
                          to maxcontig (see -d below).  The default value is
                          1, 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.

           -d rotdelay    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.

           -e maxbpg      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 cylinder 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



 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003






 tunefs(1M)                                                       tunefs(1M)




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

           -m minfree     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.

           -r advanced read-ahead
                          Advanced read-ahead specifies whether the file
                          system should use an advanced predictive readahead
 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.

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

           -A             (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    [Toc]    [Back]
      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    [Toc]    [Back]
      tunefs was developed by the University of California, Berkeley.

 SEE ALSO    [Toc]    [Back]
      dumpfs(1M), mkfs(1M), newfs(1M).


 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003