tunefs(1M) tunefs(1M)
NAME
tunefs - tune up an existing file system
SYNOPSIS
tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree]
[-o [s | space | t | time]] special | filesystem
DESCRIPTION
tunefs is designed to change the dynamic parameters of a file
system which affect the layout policies. The file system must
be unmounted before using tunefs. The parameters which are to
be changed are indicated by the options given below:
Options
-a maxcontig
Specify the maximum number of contiguous blocks that
will be laid out before forcing a rotational delay
(see -d below). 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.
-d rotdelay
Specify 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.
-e maxbpg
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 file systems with exclusively
large files, this parameter should be set higher.
Copyright 1994 Novell, Inc. Page 1
tunefs(1M) tunefs(1M)
-m minfree
Specify 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: 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. minfree also determines when the file
system will automatically switch between time
optimization and space optimization. If there are more
than (minfree -2) percent free fragments, the file
system will switch to space optimization. If minfree
is less than 5, then any switch to time optimization
will be inhibited.
-o [s | space | t | time]
Change optimization strategy for the file system. s
and space are interchangeable, and t and time are
interchangeable.
s or space Conserve space.
t or time Organize file layout to minimize access
time.
Generally one should optimize for time unless the file
system is over 90% full.
REFERENCES
mkfs(1M), sfs-specific tunefs(1M_SFS)
Copyright 1994 Novell, Inc. Page 2