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

     tunefs - tune up an existing file system

     tunefs [-A] [-a maxcontig] [-d rotdelay] [-e maxbpg] [-f avgfilesize]
            [-m minfree] [-n enable | disable] [-o space | time] [-p]
            [-s avgfpdir] [special | filesystem]

     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 super-block.
             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
             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 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
             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 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 avgfilezsize
             Specify the expected average file size.

     -m minfree
             Specify the percentage of space held back from normal users; the
             minimum free space threshold.  The default value used is 8%.
             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.  Settings of 5% and less force space optimization to
             always be used which will greatly increase the overhead for file
             writes.  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.

     -n enable | disable
             Turn on/off soft updates.  An unmounted filesystem is required.

     -o space | time
             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.  Optimization for space has much
             higher overhead 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
             in the dumpfs(8) manual page.

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

     If tunefs -n is run to enable/disable soft update on an unmounted file
     system after booting single-user then tunefs will output the warning

     reload: Invalid argument

     preceded by the raw device name.  This occurs because the filesystem is
     not currently mounted read-only.  tunefs is trying to reload the incore
     (r*) device, but it was never loaded to begin with.  When you boot single
     user, only ``/'' is mounted, so all other filesystems will give you that
     warning.  It is completely harmless.

     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).

     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.

     The tunefs command appeared in 4.2BSD.

FreeBSD 11.0-PRERELEASE        December 11, 1993       FreeBSD 11.0-PRERELEASE


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