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NAME    [Toc]    [Back]

     tunefs - tune up an existing file system

SYNOPSIS    [Toc]    [Back]

     tunefs [-Ap] [-a maxcontig] [-d rotdelay]  [-e  maxbpg]  [-f
            [-m minfree] [-n avgfpdir] [-o optimize_preference]
            [special | filesys]

DESCRIPTION    [Toc]    [Back]

     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       The  file  system has several backups of the superblock.  Specifying
 this option will cause all backups to  be  modified as well as
             the  primary  super-block.  This is potentially dangerous - use
             with caution.

     -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 depends on the block size  (4  for
16KB blocks, 8
             for  8KB blocks and 16 for 4KB blocks).  Most device
drivers can
             chain several buffers together in a single transfer.
For optimal
             performance, the value of maxcontig should be chosen
based on the
             maximum chain length supported by the device driver.

     -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 subsequently allocated  in  that
             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.

     -f avgfilesize
             Specifies  the  expected average file size in bytes.
This value
             could be used for various optimizations, but for now
it is only
             used together with avgfpdir to optimize the directory allocation
             policy.   To  take   effect,   both   avgfpdir   and
avgfilesize must be
             greater than zero.  (Also see avgfpdir.)

     -m minfree
             This  value  specifies  the percentage of space held
back from normal
 users; the minimum free  space  threshold.   The
default value
             used is 5%.  This value can be set to zero; however,
a factor of
             up to three in throughput will be lost over the performance obtained
 at a 5% 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

     -n avgfpdir
             Specifies the expected average number of  files  per
directory in
             the  file  system.   This value is used only if both
avgfilesize and
             avgfpdir are greater than zero.  It is used to limit
number of
             directories which may be allocated one after another
in the same
             cylinder  group  without  intervention  by   regular
files.  This value
             does  not  affect most file system operations but is
useful for applications
 which at first create a directory  structure and then
             populate  with files later.  (Also see avgfilesize.)

     -o optimize_preference
             The file system can either try to minimize the  time
spent allocating
  blocks,  or  it  can attempt to minimize the
space fragmentation
 on the disk.  If  the  value  of  minfree  (see
above) is less
             than  5%,  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 5%, fragmentation is unlikely to be
 and the file system can be optimized for  time.

     -p       This  option  shows  a  summary of what the current
tuneable settings
             are on the selected file system.  More detailed  information can
             be obtained in the dumpfs(8) manual page.

SEE ALSO    [Toc]    [Back]

     fs(5), dumpfs(8), growfs(8), newfs(8)

     M.  McKusick, W. Joy, S. Leffler, and R. Fabry, "A Fast File
System for
     UNIX",  ACM  Transactions  on  Computer  Systems  2,  3,  pp
181-197, August
     1984, (reprinted in the BSD System Manager's Manual, SMM:5).

HISTORY    [Toc]    [Back]

     The tunefs command appeared in 4.2BSD.

BUGS    [Toc]    [Back]

     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

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

OpenBSD     3.6                        December     11,      1993
[ Back ]
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