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

NAME
     tunefs -- tune up an existing file system

SYNOPSIS
     tunefs [-A] [-a enable | disable] [-e maxbpg] [-f avgfilesize]
            [-L volname] [-l enable | disable] [-m minfree]
            [-n enable | disable] [-o space | time] [-p] [-s avgfpdir] special
            | filesystem

DESCRIPTION
     The tunefs utility is designed to change the dynamic parameters of a file
     system which affect the layout policies.  The tunefs utility cannot be
     run on an active file system.  To change an active file system, it must
     be downgraded to read-only or unmounted.

     The parameters which are to be changed are indicated by the flags given
     below:

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

     -a enable | disable
             Turn on/off the administrative ACL enable flag.

     -e maxbpg
             Indicate the maximum number of blocks any single file can allo-
             cate out of a cylinder group before it is forced to begin allo-
             cating 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 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.

     -f avgfilesize
             Specify the expected average file size.

     -L volname
             Add/modify an optional file system volume label.

     -l enable | disable
             Turn on/off MAC multilabel flag.

     -m minfree
             Specify the percentage of space held back from normal users; the
             minimum free space threshold.  The default value used is 8%.
             Note that lowering the threshold can adversely affect perfor-
             mance:

             +o   Settings of 5% and less force space optimization to always be
                 used which will greatly increase the overhead for file
                 writes.

             +o   The file system's ability to avoid fragmentation will be
                 reduced when the total free space, including the reserve,
                 drops below 15%.  As free space approaches zero, throughput
                 can degrade by up to a factor of three over the performance
                 obtained at a 10% threshold.

             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.

     -n enable | disable
             Turn on/off soft updates.

     -o space | time
             The file system can either try to minimize the time spent allo-
             cating blocks, or it can attempt to minimize the space fragmenta-
             tion on the disk.  Optimization for space has much higher over-
             head for file writes.  The kernel normally changes the preference
             automatically as the percent fragmentation changes on the file
             system.

     -p      Show a summary of what the current tunable settings are on the
             selected file system.  More detailed information can be obtained
             from the dumpfs(8) utility.

     -s avgfpdir
             Specify the expected number of files per directory.

     At least one of the above flags is required.

FILES
     /etc/fstab  read this to determine the device file for a specified mount
                 point.

SEE ALSO
     fs(5), dumpfs(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
     The tunefs utility appeared in 4.2BSD.

BUGS
     This utility should work on active file systems.

     You can tune a file system, but you cannot tune a fish.

FreeBSD 6.2                      May 18, 2002                      FreeBSD 6.2

NAME | SYNOPSIS | DESCRIPTION | FILES | SEE ALSO | HISTORY | BUGS

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