TUNEFS(8) BSD System Manager's Manual TUNEFS(8)NAMEtunefs — tune up an existing UFS filesystem
SYNOPSIStunefs [-Ap] [-a maxcontig] [-d rotdelay] [-e maxbpg] [-f avgfilesize]
[-m minfree] [-n enable | disable] [-o space | time] [-s avgfpdir]
{special | filesystem}
DESCRIPTION
Tunefs is designed to change the dynamic parameters of a filesystem which
affect the layout policies. The parameters which are to be changed are
indicated by the flags given below:
-A The filesystem 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
with caution.
-a maxcontig
Specify 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 inter‐
rupt per disk transfer. Device drivers that can chain several
buffers together in a single transfer should set this to the max‐
imum chain length.
-d rotdelay
Specify 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.
-e maxbpg
Indicate the maximum number of blocks any single file can allo‐
cate out of a cylinder group before it is forced to begin allo‐
cating blocks from another cylinder group. Typically this value
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
filesystems with exclusively large files, this parameter should
be set higher.
-f avgfilezsize
Specify the expected average file size.
-m minfree
Specify the percentage of space held back from normal users; the
minimum free space threshold. The default value used is 8%.
This value can be set to zero, however up to a factor of three in
throughput will be lost over the performance obtained at a 10%
threshold. Settings of 5% and less force space optimization to
always be used which will greatly increase the overhead for file
writes. 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 higher threshold.
-n enable | disable
Turn on/off soft updates.
-o space | time
The filesystem can either try to minimize the time spent allocat‐
ing blocks, or it can attempt to minimize the space fragmentation
on the disk. Optimization for space has much higher overhead for
file writes. The kernel normally changes the preference automat‐
ically as the percent fragmentation changes on the filesystem.
-p Show a summary of what the current tunable settings are on the
selected filesystem. More detailed information can be obtained
in the dumpfs(8) manual page.
-s avgfpdir
Specify the expected number of files per directory.
FILES
/etc/fstab read this to determine the device file for a specified mount
point.
SEE ALSOfs(5), UFS(5), dumpfs(8), newfs(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).
HISTORY
The tunefs command appeared in 4.2BSD.
BUGS
This program should work on mounted and active filesystems. Because the
super-block is not kept in the buffer cache, the changes will only take
effect if the program is run on dismounted filesystems. To change the
root filesystem, the system must be rebooted after the filesystem is
tuned.
You can tune a filesystem, but you can't tune a fish.
BSD December 11, 1993 BSD
