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TUNEFS(8)                   System Manager's Manual                  TUNEFS(8)

       tunefs - tune up an existing file system

       /etc/tunefs tuneup-options special|filesys

       Tunefs  is  designed  to change the dynamic parameters of a file system
       which affect the layout 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 sev-
              eral  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 degrad-
              ing  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 else-
              where.   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 nor-
              mal  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
              files until enough files have been  deleted  to  get  under  the
              higher threshold.

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

       McKusick, Joy, Leffler; "A Fast File System for Unix", Computer Systems
       Research Group, Dept of EECS, Berkeley,  CA  94720;  TR  #7,  September

       This  program  should work on mounted and active file systems.  Because
       the super-block is not kept in the buffer cache, the program will  only
       take  effect  if  it is run on dismounted file systems.  (if run on the
       root file system, the system must be rebooted)

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

4th Berkeley Distribution      20 February 1983                      TUNEFS(8)