Manual page for TUNEFS(8)
tunefs - tune up an existing (dismounted) file system
special | filesystem
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
- -a maxcontig
This specifies the maximum number of blocks, belonging to
the same file, that will be
allocated contiguously before inserting a rotational delay (see
Formerly, this value was always 1 because neither the device drivers
nor the Unix file system (UFS) could handle multiple block requests.
UFS has been modified to cluster together several (up to
blocks when doing sequential
reads and writes, resulting in higher I/O rates. This is especially
beneficial on drives or controllers with track buffers; in some cases it can
double or triple the I/O rates.
sets the value to 7 for many drives, but
the best value varies from drive to drive because of the track buffer size
as well as the drive geometry. People interested in the getting the
utmost performace from their drives can try something like this
(note that only the
read case is of interest - the write case goes into the cache):
for i in 1 2 3 4 5 6 7
do umount /mnt
tunefs -a $i /mnt
dd if=/dev/zero of=/mnt/XXX bs=8k count=1000
umount /mnt; mount /mnt # to clear the cache
time dd of=/dev/null if=/mnt/XXX bs=8k
This parameter is limited in the following way:
blocksize * maxcontig must be <= maxphys
is a read-only kernel variable that specifies
the maximum block transfer size (in bytes) that
the I/O subsystem is capable of satisfying. On most machines,
is 56 Kbytes; on the
architecture it is currently 124 Kbytes which allows
to vary from 1 to 15. This value is subject to change.
(The limit is enforced by
- -d rotdelay
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.
For drives with track buffers a
of 0 is usually the best choice.
- -e maxbpg
This indicates the maximum number of blocks any single file can
allocate out of a cylinder group before it is forced to begin
allocating 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 file systems with exclusively large files,
this parameter should be set higher.
- -m minfree
This value specifies the percentage of space held back
from normal users; the minimum free space threshold.
The default value used is 10%.
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%
Note: 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.
[a manual with the abbreviation ADMIN]
This program should work on mounted and active file systems.
Because the super-block is not kept in the buffer cache,
the program will only take effect if it
is run on dismounted file systems;
if run on the root file system, the system must be rebooted.
You can tune a file system, but you can't tune a fish.
Created by unroff & hp-tools.
© by Hans-Peter Bischof. All Rights Reserved (1997).
Last modified 21/April/97