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BSD 2.11 - man page for tunefs (bsd section 8)

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TUNEFS(8)										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 lay-
       out policies.  The parameters 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 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 subse-
	      quently 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
	      This value specifies the percentage of space held back from normal users; the mini-
	      mum 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 perfor-
	      mance obtained at a 10% threshold.  Note that if the value is raised above the cur-
	      rent  usage  level,  users will be unable to allocate 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 minfree
	      (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 problematical, 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 Transac-
       tions on Computer Systems 2, 3.	pp 181-197, August 1984.  (reprinted in the  System  Man-
       ager'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.

4.2 Berkeley Distribution		November 17, 1996				TUNEFS(8)
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