tunefs - Tunes an existing UFS file system
/usr/sbin/tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg]
[-m minfree] [-o optimization_preference] file_system
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 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 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.
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 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 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.
Commands: newfs(8)
tunefs(8)
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