1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)tunefs.8 8.2 (Berkeley) 12/11/93 33.\" $FreeBSD$ 34.\" 35.Dd December 11, 1993 36.Dt TUNEFS 8 37.Os 38.Sh NAME 39.Nm tunefs 40.Nd tune up an existing file system 41.Sh SYNOPSIS 42.Nm 43.Op Fl A 44.Op Fl a Ar maxcontig 45.Op Fl d Ar rotdelay 46.Op Fl e Ar maxbpg 47.Op Fl f Ar avgfilesize 48.Op Fl m Ar minfree 49.Bk -words 50.Op Fl n Ar enable | disable 51.Op Fl o Ar space | time 52.Op Fl p 53.Op Fl s Ar avgfpdir 54.Ek 55.Ar special | Ar filesystem 56.Sh DESCRIPTION 57.Nm Tunefs 58is designed to change the dynamic parameters of a file system 59which affect the layout policies. 60The parameters which are to be changed are indicated by the flags 61given below: 62.Bl -tag -width indent 63.It Fl A 64The file system has several backups of the super-block. Specifying 65this option will cause all backups to be modified as well as the 66primary super-block. This is potentially dangerous - use with caution. 67.It Fl a Ar maxcontig 68Specify the maximum number of contiguous blocks that will 69be laid out before forcing a rotational delay (see 70.Fl d 71below). 72The default value is one, since most device drivers require 73an interrupt per disk transfer. 74Device drivers that can chain several buffers together in a single 75transfer should set this to the maximum chain length. 76.It Fl d Ar rotdelay 77Specify the expected time (in milliseconds) 78to service a transfer completion 79interrupt and initiate a new transfer on the same disk. 80It is used to decide how much rotational spacing to place between 81successive blocks in a file. 82.It Fl e Ar maxbpg 83Indicate the maximum number of blocks any single file can 84allocate out of a cylinder group before it is forced to begin 85allocating blocks from another cylinder group. 86Typically this value is set to about one quarter of the total blocks 87in a cylinder group. 88The intent is to prevent any single file from using up all the 89blocks in a single cylinder group, 90thus degrading access times for all files subsequently allocated 91in that cylinder group. 92The effect of this limit is to cause big files to do long seeks 93more frequently than if they were allowed to allocate all the blocks 94in a cylinder group before seeking elsewhere. 95For file systems with exclusively large files, 96this parameter should be set higher. 97.It Fl f Ar avgfilezsize 98Specify the expected average file size. 99.It Fl m Ar minfree 100Specify the percentage of space held back 101from normal users; the minimum free space threshold. 102The default value used is 8%. 103Note that lowering the threshold can adversely affect performance: 104.Pp 105.Bl -bullet 106.It 107Settings of 5% and less force space optimization to 108always be used which will greatly increase the overhead for file 109writes. 110.It 111The filesystem's ability to avoid fragmentation will be reduced 112when the total free space, including the reserve, drops below 15%. 113As free space approaches zero, throughput can degrade by up to a 114factor of three over the performance obtained at a 10% threshold. 115.El 116.Pp 117If the value is raised above the current usage level, 118users will be unable to allocate files until enough files have 119been deleted to get under the higher threshold. 120.It Fl n Ar enable | disable 121Turn on/off soft updates. 122An unmounted filesystem is required. 123.It Fl o Ar space | time 124The file system can either try to minimize the time spent 125allocating blocks, or it can attempt to minimize the space 126fragmentation on the disk. 127Optimization for space has much 128higher overhead for file writes. 129The kernel normally changes the preference automatically as 130the percent fragmentation changes on the file system. 131.It Fl p 132Show a summary of what the current tunable settings 133are on the selected file system. More detailed information can be 134obtained in the 135.Xr dumpfs 8 136manual page. 137.It Fl s Ar avgfpdir 138Specify the expected number of files per directory. 139.El 140.Pp 141At least one of the above flags is required. 142.Sh SEE ALSO 143.Xr fs 5 , 144.Xr dumpfs 8 , 145.Xr newfs 8 146.Rs 147.%A M. McKusick 148.%A W. Joy 149.%A S. Leffler 150.%A R. Fabry 151.%T "A Fast File System for UNIX" 152.%J "ACM Transactions on Computer Systems 2" 153.%N 3 154.%P pp 181-197 155.%D August 1984 156.%O "(reprinted in the BSD System Manager's Manual, SMM:5)" 157.Re 158.Sh BUGS 159This program should work on mounted and active file systems. 160Because the super-block is not kept in the buffer cache, 161the changes will only take effect if the program 162is run on dismounted file systems. 163To change the root file system, the system must be rebooted 164after the file system is tuned. 165.\" Take this out and a Unix Demon will dog your steps from now until 166.\" the time_t's wrap around. 167.Pp 168You can tune a file system, but you can't tune a fish. 169.Sh HISTORY 170The 171.Nm 172command appeared in 173.Bx 4.2 . 174