tunefs(8)tunefs(8)NAMEtunefs - Tunes an existing UFS file system
SYNOPSIS
/usr/sbin/tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree]
[-o optimization_preference] file_system
OPTIONS
Specifies the maximum number of contiguous blocks that will be laid out
before forcing a rotational delay (see the -d option). The default
value is 8. Device drivers that can chain several buffers together in a
single transfer should set this to the maximum chain length. 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. Indicates the maximum number of blocks any single file can
allocate out of a cylinder group before it is forced to begin allocat‐
ing blocks from another cylinder group. Typically, you set this value
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 subse‐
quently 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 parame‐
ter should be set higher. 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%
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 higher threshold. Specifies whether the
file system should try to minimize the time spent allocating blocks (-o
time) or try to minimize the space fragmentation on the disk (-o
space).
If the value of minfree (see the previous list item) 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 a
problem, and the file system can be optimized for time.
OPERANDS
Specifies the UFS file system that is being tuned.
DESCRIPTION
The tunefs command changes the dynamic parameters of a UFS file system
that affect the layout policies. The parameters to be changed are indi‐
cated by the options specified.
You should unmount a file system before running the tunefs program. The
tunefs program does allow you to enter parameters for a mounted and
active file system. However, your changes will not take effect until
the file system is unmounted and mounted again (or until after the sys‐
tem is rebooted). If you use tunefs to tune the root file system
(assuming root is a UFS file system), you must always reboot the system
in order for your changes to take effect.
For larger-capacity devices, set minfree to five percent.
The rotdelay value is useful for disks that do not have read-ahead
cache, such as the RA-series disks. For disks that have read-ahead
cache, set rotdelay to zero.
After you specify an optimization preference, it comes into play only
under the following conditions: A file is growing It is not possible to
extend a fragment There is a choice between allocating an exact-sized
fragment or allocating a full block and freeing the unused portion of
the block
After you specify an optimization preference, the system first tries
the specified preference when it reaches the minimum reserved space
specified by the minfree value. If you specified -o space, the system
tries space optimization, but switches to time optimization if the file
continues to grow and fragmentation is less than half of the minimum
free reserve. If you specifed -o time, the system tries time optimiza‐
tion, but switches to space optimization if the file growth causes disk
fragmentation to reach within two percent of the minimum free reserve.
You must be the root user to use this command.
FILES
Specifies the command path.
SEE ALSO
Commands: newfs(8)tunefs(8)
