tunefs(1M)                                                       tunefs(1M)


   NAME
         tunefs - tune up an existing file system

   SYNOPSIS
         tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree] [-o
         [space | 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


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   tunefs(1M)                                                       tunefs(1M)


                 under the higher threshold.

        -o [space | time]
                 Change optimization strategy for the file system.
                 s - space (conserve space)
                 t - 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), ufs(4).  fork(2), terminfo(4) in the Programmer's Reference
         Manual.







































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