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1.\" Copyright (c) 1983, 1991, 1993
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32.\" @(#)tunefs.8 8.2 (Berkeley) 12/11/93
33.\" $FreeBSD: src/sbin/tunefs/tunefs.8,v 1.11.2.6 2003/01/23 11:14:02 maxim Exp $
1de703da 34.\" $DragonFly: src/sbin/tunefs/tunefs.8,v 1.2 2003/06/17 04:27:34 dillon Exp $
984263bc
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35.\"
36.Dd December 11, 1993
37.Dt TUNEFS 8
38.Os
39.Sh NAME
40.Nm tunefs
41.Nd tune up an existing filesystem
42.Sh SYNOPSIS
43.Nm
44.Op Fl A
45.Op Fl a Ar maxcontig
46.Op Fl d Ar rotdelay
47.Op Fl e Ar maxbpg
48.Op Fl f Ar avgfilesize
49.Op Fl m Ar minfree
50.Bk -words
51.Op Fl n Ar enable | disable
52.Op Fl o Ar space | time
53.Op Fl p
54.Op Fl s Ar avgfpdir
55.Ek
56.Op Ar special | Ar filesystem
57.Sh DESCRIPTION
58.Nm Tunefs
59is designed to change the dynamic parameters of a filesystem
60which affect the layout policies.
61The parameters which are to be changed are indicated by the flags
62given below:
63.Bl -tag -width indent
64.It Fl A
65The filesystem has several backups of the super-block. Specifying
66this option will cause all backups to be modified as well as the
67primary super-block. This is potentially dangerous - use with caution.
68.It Fl a Ar maxcontig
69Specify the maximum number of contiguous blocks that will
70be laid out before forcing a rotational delay (see
71.Fl d
72below).
73The default value is one, since most device drivers require
74an interrupt per disk transfer.
75Device drivers that can chain several buffers together in a single
76transfer should set this to the maximum chain length.
77.It Fl d Ar rotdelay
78Specify the expected time (in milliseconds)
79to service a transfer completion
80interrupt and initiate a new transfer on the same disk.
81It is used to decide how much rotational spacing to place between
82successive blocks in a file.
83.It Fl e Ar maxbpg
84Indicate the maximum number of blocks any single file can
85allocate out of a cylinder group before it is forced to begin
86allocating blocks from another cylinder group.
87Typically this value is set to about one quarter of the total blocks
88in a cylinder group.
89The intent is to prevent any single file from using up all the
90blocks in a single cylinder group,
91thus degrading access times for all files subsequently allocated
92in that cylinder group.
93The effect of this limit is to cause big files to do long seeks
94more frequently than if they were allowed to allocate all the blocks
95in a cylinder group before seeking elsewhere.
96For filesystems with exclusively large files,
97this parameter should be set higher.
98.It Fl f Ar avgfilezsize
99Specify the expected average file size.
100.It Fl m Ar minfree
101Specify the percentage of space held back
102from normal users; the minimum free space threshold.
103The default value used is 8%.
104This value can be set to zero, however up to a factor of three
105in throughput will be lost over the performance obtained at a 10%
106threshold.
107Settings of 5% and less force space optimization to
108always be used which will greatly increase the overhead for file
109writes.
110Note that if the value is raised above the current usage level,
111users will be unable to allocate files until enough files have
112been deleted to get under the higher threshold.
113.It Fl n Ar enable | disable
114Turn on/off soft updates.
115.It Fl o Ar space | time
116The filesystem can either try to minimize the time spent
117allocating blocks, or it can attempt to minimize the space
118fragmentation on the disk.
119Optimization for space has much
120higher overhead for file writes.
121The kernel normally changes the preference automatically as
122the percent fragmentation changes on the filesystem.
123.It Fl p
124Show a summary of what the current tunable settings
125are on the selected filesystem. More detailed information can be
126obtained in the
127.Xr dumpfs 8
128manual page.
129.It Fl s Ar avgfpdir
130Specify the expected number of files per directory.
131.El
132.Sh FILES
133.Bl -tag -width /etc/fstab -compact
134.It Pa /etc/fstab
135read this to determine the device file for a
136specified mount point.
137.El
138.Sh SEE ALSO
139.Xr fs 5 ,
140.Xr dumpfs 8 ,
141.Xr newfs 8
142.Rs
143.%A M. McKusick
144.%A W. Joy
145.%A S. Leffler
146.%A R. Fabry
147.%T "A Fast File System for UNIX"
148.%J "ACM Transactions on Computer Systems 2"
149.%N 3
150.%P pp 181-197
151.%D August 1984
152.%O "(reprinted in the BSD System Manager's Manual, SMM:5)"
153.Re
154.Sh BUGS
155This program should work on mounted and active filesystems.
156Because the super-block is not kept in the buffer cache,
157the changes will only take effect if the program
158is run on dismounted filesystems.
159To change the root filesystem, the system must be rebooted
160after the filesystem is tuned.
161.\" Take this out and a Unix Demon will dog your steps from now until
162.\" the time_t's wrap around.
163.Pp
164You can tune a filesystem, but you can't tune a fish.
165.Sh HISTORY
166The
167.Nm
168command appeared in
169.Bx 4.2 .