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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.  To change the root file
     system, the system	must be	rebooted after the file	system is tuned.

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

FreeBSD	9.3			August 13, 2007			   FreeBSD 9.3

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

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