138 lines
5.3 KiB
Groff
138 lines
5.3 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)tunefs.8 8.2 (Berkeley) 12/11/93
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.\"
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.Dd December 11, 1993
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.Dt TUNEFS 8
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.Os BSD 4.2
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.Sh NAME
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.Nm tunefs
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.Nd tune up an existing file system
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.Sh SYNOPSIS
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.Nm tunefs
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.Op Fl a Ar maxcontig
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.Op Fl d Ar rotdelay
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.Op Fl e Ar maxbpg
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.Op Fl m Ar minfree
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.Bk -words
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.Op Fl o Ar optimize_preference
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.Ek
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.Op Ar special | Ar filesys
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.Sh DESCRIPTION
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.Nm Tunefs
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is designed to change the dynamic parameters of a file system
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which affect the layout policies.
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The parameters which are to be changed are indicated by the flags
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given below:
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.Bl -tag -width Ds
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.It Fl a Ar maxcontig
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This specifies the maximum number of contiguous blocks that will
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be laid out before forcing a rotational delay (see
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.Fl d
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below).
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The default value is one, since most device drivers require
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an interrupt per disk transfer.
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Device drivers that can chain several buffers together in a single
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transfer should set this to the maximum chain length.
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.It Fl d Ar rotdelay
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This specifies the expected time (in milliseconds)
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to service a transfer completion
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interrupt and initiate a new transfer on the same disk.
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It is used to decide how much rotational spacing to place between
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successive blocks in a file.
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.It Fl e Ar maxbpg
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This indicates the maximum number of blocks any single file can
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allocate out of a cylinder group before it is forced to begin
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allocating blocks from another cylinder group.
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Typically this value is set to about one quarter of the total blocks
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in a cylinder group.
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The intent is to prevent any single file from using up all the
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blocks in a single cylinder group,
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thus degrading access times for all files subsequently allocated
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in that cylinder group.
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The effect of this limit is to cause big files to do long seeks
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more frequently than if they were allowed to allocate all the blocks
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in a cylinder group before seeking elsewhere.
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For file systems with exclusively large files,
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this parameter should be set higher.
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.It Fl m Ar minfree
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This value specifies the percentage of space held back
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from normal users; the minimum free space threshold.
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The default value used is 8%.
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This value can be set to zero, however up to a factor of three
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in throughput will be lost over the performance obtained at a 10%
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threshold. Settings of 5% and less force space optimization to
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always be used which will greatly increase the overhead for file
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writes.
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Note that if the value is raised above the current usage level,
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users will be unable to allocate files until enough files have
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been deleted to get under the higher threshold.
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.It Fl o Ar optimize_preference
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The file system can either try to minimize the time spent
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allocating blocks, or it can attempt to minimize the space
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fragmentation on the disk. Optimization for space has much
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higher overhead for file writes.
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The kernel normally changes the preference automatically as
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the percent fragmentation changes on the file system.
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.El
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.Sh SEE ALSO
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.Xr fs 5 ,
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.Xr dumpfs 8 ,
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.Xr newfs 8 ,
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.Xr mkfs 8
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.Rs
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.%A M. McKusick
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.%A W. Joy
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.%A S. Leffler
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.%A R. Fabry
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.%T "A Fast File System for UNIX"
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.%J "ACM Transactions on Computer Systems 2"
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.%N 3
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.%P pp 181-197
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.%D August 1984
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.%O "(reprinted in the BSD System Manager's Manual, SMM:5)"
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.Re
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.Sh BUGS
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This program should work on mounted and active file systems.
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Because the super-block is not kept in the buffer cache,
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the changes will only take effect if the program
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is run on dismounted file systems.
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To change the root file system, the system must be rebooted
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after the file system is tuned.
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.Pp
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You can tune a file system, but you can't tune a fish.
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.Sh HISTORY
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The
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.Nm
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command appeared in
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.Bx 4.2 .
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