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 BSD 4.2 38.Sh NAME 39.Nm tunefs 40.Nd tune up an existing file system 41.Sh SYNOPSIS 42.Nm tunefs 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 m Ar minfree 48.Bk -words 49.Op Fl n Ar enable | disable 50.Op Fl o Ar optimize_preference 51.Op Fl p 52.Ek 53.Op Ar special | Ar filesystem 54.Sh DESCRIPTION 55.Nm Tunefs 56is designed to change the dynamic parameters of a file system 57which affect the layout policies. 58The parameters which are to be changed are indicated by the flags 59given below: 60.Bl -tag -width indent 61.It Fl A 62The file system has several backups of the super-block. Specifying 63this option will cause all backups to be modified as well as the 64primary super-block. This is potentially dangerous - use with caution. 65.It Fl a Ar maxcontig 66Specify the maximum number of contiguous blocks that will 67be laid out before forcing a rotational delay (see 68.Fl d 69below). 70The default value is one, since most device drivers require 71an interrupt per disk transfer. 72Device drivers that can chain several buffers together in a single 73transfer should set this to the maximum chain length. 74.It Fl d Ar rotdelay 75Specify the expected time (in milliseconds) 76to service a transfer completion 77interrupt and initiate a new transfer on the same disk. 78It is used to decide how much rotational spacing to place between 79successive blocks in a file. 80.It Fl e Ar maxbpg 81Indicate the maximum number of blocks any single file can 82allocate out of a cylinder group before it is forced to begin 83allocating blocks from another cylinder group. 84Typically this value is set to about one quarter of the total blocks 85in a cylinder group. 86The intent is to prevent any single file from using up all the 87blocks in a single cylinder group, 88thus degrading access times for all files subsequently allocated 89in that cylinder group. 90The effect of this limit is to cause big files to do long seeks 91more frequently than if they were allowed to allocate all the blocks 92in a cylinder group before seeking elsewhere. 93For file systems with exclusively large files, 94this parameter should be set higher. 95.It Fl m Ar minfree 96Specify the percentage of space held back 97from normal users; the minimum free space threshold. 98The default value used is 8%. 99This value can be set to zero, however up to a factor of three 100in throughput will be lost over the performance obtained at a 10% 101threshold. Settings of 5% and less force space optimization to 102always be used which will greatly increase the overhead for file 103writes. 104Note that if the value is raised above the current usage level, 105users will be unable to allocate files until enough files have 106been deleted to get under the higher threshold. 107.It Fl n Ar enable | disable 108Turn on/off soft updates. An unmounted filesystem is required. 109.It Fl o Ar optimize_preference 110The file system can either try to minimize the time spent 111allocating blocks, or it can attempt to minimize the space 112fragmentation on the disk. Optimization for space has much 113higher overhead for file writes. 114The kernel normally changes the preference automatically as 115the percent fragmentation changes on the file system. 116.It Fl p 117Show a summary of what the current tunable settings 118are on the selected file system. More detailed information can be 119obtained in the 120.Xr dumpfs 8 121manual page. 122.El 123.Sh SEE ALSO 124.Xr fs 5 , 125.Xr dumpfs 8 , 126.Xr newfs 8 127.Rs 128.%A M. McKusick 129.%A W. Joy 130.%A S. Leffler 131.%A R. Fabry 132.%T "A Fast File System for UNIX" 133.%J "ACM Transactions on Computer Systems 2" 134.%N 3 135.%P pp 181-197 136.%D August 1984 137.%O "(reprinted in the BSD System Manager's Manual, SMM:5)" 138.Re 139.Sh BUGS 140This program should work on mounted and active file systems. 141Because the super-block is not kept in the buffer cache, 142the changes will only take effect if the program 143is run on dismounted file systems. 144To change the root file system, the system must be rebooted 145after the file system is tuned. 146.\" Take this out and a Unix Demon will dog your steps from now until 147.\" the time_t's wrap around. 148.Pp 149You can tune a file system, but you can't tune a fish. 150.Sh HISTORY 151The 152.Nm 153command appeared in 154.Bx 4.2 . 155