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TUNEFS(8) OpenBSD System Manager's Manual TUNEFS(8)
tunefs - tune up an existing file system
tunefs [-A] [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree]
[-o optimize_preference] [-s enable | disable] [special | filesys]
Tunefs is designed to change the dynamic parameters of a file system
which affect the layout policies. The parameters which are to be changed
are indicated by the flags given below:
-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
This specifies the maximum number of contiguous blocks that will
be laid out before forcing a rotational delay (see -d below).
The default value is one, since most device drivers require an
interrupt per disk transfer. Device drivers that can chain sev-
eral buffers together in a single transfer should set this to the
maximum chain length.
This specifies the expected time (in milliseconds) to service a
transfer completion interrupt and initiate a new transfer on the
same disk. It is used to decide how much rotational spacing to
place between successive blocks in a file.
This indicates the maximum number of blocks any single file can
allocate out of a cylinder group before it is forced to begin al-
locating blocks from another cylinder group. Typically this val-
ue 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.
This value specifies the percentage of space held back from nor-
mal users; the minimum free space threshold. The default value
used is 10%. This value can be set to zero, however up to a fac-
tor of three in throughput will be lost over the performance ob-
tained at a 10% threshold. Note that 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 high-
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. If the value of minfree (see above) is less
than 10%, then the file system should optimize for space to avoid
running out of full sized blocks. For values of minfree greater
than or equal to 10%, fragmentation is unlikely to be problemati-
cal, and the file system can be optimized for time.
-p This option shows a summary of what the current tuneable settings
are on the selected file system. More detailed information can
be obtained in the dumpfs(8) manual page.
This option enables soft updates on the file system. Soft updates
eliminates most synchronous writes to disk by maintaining a par-
tial order of writes to the disk. This significantly improves
meta-data operations (file creation and deletion) at the expense
of subjecting them to the same potential 30-second delay as file
data. Recovery is made simpler, however, by maintaining a strict
ordering of writes to disk.
fs(5), dumpfs(8), newfs(8), mkfs(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).
This program should work on mounted and active file systems. Because the
super-block is not kept in the buffer cache, the changes will only take
effect if the program is run on dismounted file systems. To change the
root file system, the system must be rebooted after the file system is
You can tune a file system, but you can't tune a fish.
The tunefs command appeared in 4.2BSD.
4.2 Berkeley Distribution December 11, 1993 2
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.
(Corrections, notes, and links courtesy of RocketAware.com)
FreeBSD Sources for tunefs(8)
OpenBSD sources for tunefs(8)
Up to: File System Operations - Operations for entire file-systems (quotas, configuration, consistency, mount, unmount, et al)
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