tunefs - Tunes an existing UFS file system
/usr/sbin/tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree] [-o
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 succes-
sive 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 allocating 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 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
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
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.
Specifies the UFS file system that is being tuned.
The tunefs command changes the dynamic parameters of a UFS file system that
affect the layout policies. The parameters to be changed are indicated 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 system 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 allo-
cating 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 optimization, 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.
Specifies the command path.