tunefs(1M)        MISC. REFERENCE MANUAL PAGES         tunefs(1M)



NAME
     tunefs - tune up an existing file system

SYNOPSIS
     tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree]
     [-o [s | t]] special | filesystem

DESCRIPTION
     tunefs is designed to change the  dynamic  parameters  of  a
     file system which affect the layout policies.  The file sys-
     tem 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  ser-
             vice  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 succes-
             sive 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  nor-
             mal  users;  the  minimum free space threshold.  The



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

     -o [s | t]
             Change optimization strategy for the file system.

             s - space (conserve space)
             t - time (attempt to organize file layout to  minim-
             ize  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.




































                        Last change: UFS                        2