tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-o [s | space | t | time]] special | filesystem
is designed to change the dynamic parameters
of a filesystem which affect the layout policies.
The filesystem must be unmounted before using tunefs.
The parameters which are to be changed are indicated
by the options given below:
The options are:
Specify the maximum number of contiguous
blocks that will be laid out before forcing
a rotational delay (see
The default value is one,
since most device drivers require
an interrupt per disk transfer.
Device drivers that can chain several buffers
together in a single transfer should set this to the
maximum chain length.
Specify the expected time (in milliseconds)
to service a transfer completion
interrupt and initiate a new transfer on the
It is used to decide how much rotational spacing to
place between successive blocks in a file.
Indicate 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 approximately
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.
-o [s | space | t | time]
Change optimization strategy for the filesystem.
s and space
are interchangeable, and t and time are interchangeable.
s or space
t or time
Organize file layout to minimize access time.
Generally one should optimize for time unless the filesystem
is over 90% full.