# 2.11BSD#431 - /usr/man/cat8/tunefs.0

    TUNEFS(8)	    UNIX Programmer's Manual		TUNEFS(8)

    NAME
         tunefs - tune up an existing file system

    SYNOPSIS
         tunefs tuneup-options special|filesys

    DESCRIPTION
         Tunefs is designed to change the dynamic parameters of a
         file system which affect the layout policies.  The parame-
         ters which are to be changed are indicated by the flags
         given below:

         -a maxcontig
    	  This specifies 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
    	  This 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
    	  This 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 this value is set to about one quar-
    	  ter 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 sys-
    	  tems with exclusively large files, this parameter
    	  should be set higher.

         -m minfree
    	  This value 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

    Printed 11/24/99	November 17, 1996			1

    TUNEFS(8)	    UNIX Programmer's Manual		TUNEFS(8)

    	  files until enough files have been deleted to get under
    	  the higher threshold.

         -o optimization preference
    	  The file system can either try to minimize the time
    	  spent allocating blocks, or it can attempt minimize the
    	  space fragmentation on the disk.  If the value of min-
    	  free (see above) 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 prob-
    	  lematical, and the file system can be optimized for
    	  time.

    SEE ALSO
         fs(5), newfs(8), mkfs(8)

         M. McKusick, W. Joy, S. Leffler, R. Fabry, ``A Fast File
         System for UNIX'', ACM Transactions on Computer Systems 2,
         3.  pp 181-197, August 1984.  (reprinted in the System
         Manager's Manual, SMM:14)

    BUGS
         This program should work on mounted and active file systems.
         Because the super-block is not kept in the buffer cache, the
         changes will only take effect if the program is run on
         dismounted file systems.  To change the root file system,
         the system must be rebooted after the file system is tuned.

         tunefs is not currently implemented in 2.11BSD.

         You can tune a file system, but you can't tune a fish.

    Printed 11/24/99	November 17, 1996			2

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