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

     tunefs -- tune up an existing UFS file system

     tunefs [-A] [-a enable | disable] [-e maxbpg] [-f avgfilesize]
	    [-j	enable | disable] [-J enable | disable]
	    [-k	held-for-metadata-blocks] [-L volname] [-l enable | disable]
	    [-m	minfree] [-N enable | disable] [-n enable | disable]
	    [-o	space |	time] [-p] [-s avgfpdir] [-S size]
	    [-t	enable | disable] special | filesystem

     The tunefs	utility	is designed to change the dynamic parameters of	a UFS
     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

     -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 POSIX.1e 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.

     -j	enable | disable
	     Turn on/off soft updates journaling.

     -J	enable | disable
	     Turn on/off gjournal flag.

     -k	held-for-metadata-blocks
	     Set the amount of space to	be held	for metadata blocks.  When
	     set, the file system preference routines will try to save the
	     specified amount of space immediately following the inode blocks
	     in	each cylinder group for	use by metadata	blocks.	 Clustering
	     the metadata blocks speeds	up random file access and decreases
	     the running time of fsck(8).  While this option can be set	at any
	     time, it is most effective	if set before any data is loaded into
	     the file system.  By default newfs(8) sets	it to half of the
	     space reserved to minfree.

     -L	volname
	     Add/modify	an optional file system	volume label.  Legal charac-
	     ters are alphanumerics, dashes, and underscores.

     -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-

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

	     o	 The file system's ability to avoid fragmentation will be re-
		 duced when the	total free space, including the	reserve, drops
		 below 15%.  As	free space approaches zero, throughput can de-
		 grade by up to	a factor of three over the performance ob-
		 tained	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 the administrative NFSv4 ACL enable flag.

     -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

     -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.

     -S	size
	     Specify the softdep journal size in bytes.	 The minimum is	4M.

     -t	enable | disable
	     Turn on/off the TRIM enable flag.	If enabled, and	if the under-
	     lying device supports the BIO_DELETE command, the file system
	     will send a delete	request	to the underlying device for each
	     freed block.  The trim enable flag	is typically set when the un-
	     derlying device uses flash-memory as the device can use the
	     delete command to pre-zero	or at least avoid copying blocks that
	     have been deleted.

	     Note that this does not trim blocks that are already free.	 See
	     the fsck_ffs(8) -E	flag.

     At	least one of these flags is required.

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

     fs(5), dumpfs(8), gjournal(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).

     The tunefs	utility	appeared in 4.2BSD.

     This utility does not 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	13.0		       January 29, 2019			  FreeBSD 13.0


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