tunefs(1M) tunefs(1M)
NAME
tunefs - tune up an existing UFS file system
SYNOPSIS
tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree] [-o
{space | time}]
special | filesystem
DESCRIPTION
tunefs is designed to change the dynamic parameters of a file system,
which determine the layout of a file system. The file system must be
unmounted beforehand with tunefs. The parameters to be modified are
indicated by the options given below.
When a ufs file system is created with newfs, these parameters can be
set as required. These parameters should only be modified for special
applications and can only be modified by system administrators, who
have very good knowledge of how ufs file systems are organized.
OPTIONS
-a maxcontig Specifies the maximum number of contiguous blocks that
can be transferred before the disk access is inter-
rupted. The default value is one, since most device
drivers require one interrupt per disk transfer. For
device drivers that can chain several blocks together in
a single transfer, you should enter the maximum length
for this type of chain. In the case of RM400, RM600-xx,
and RM600 systems, this value is always 1.
-d rotdelay Specifies the expected time (in milliseconds) to com-
plete a transfer and initiate a new transfer on the same
disk. This value is used to decide how much rotational
spacing to place between successive blocks in a file.
-e maxbpg 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, the value for maxbpg is approximately 25% of
the total blocks in a cylinder group.
This option is used to prevent any single file from
using up all the blocks in a single cylinder group, thus
degrading access times for all files subsequently allo-
cated 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 seek-
ing elsewhere. For file systems with exclusively large
files, this parameter should be set higher.
-m minfree Specifies the percentage of space retained for normal
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tunefs(1M) tunefs(1M)
users. As soon as the capacity of the file system
reaches this threshold, only an authorized user can
allocate space for files. The default value is 10%.
If the specified value exceeds the current usage level,
users will be unable to allocate files until enough
files have been deleted to get under the higher thres-
hold.
The threshold can also be set to zero, however up to a
factor of three in throughput will be lost compared to
the performance obtained at 10%.
-o {space | time}
Changes optimization strategy for the file system. (The
optimization strategy can be defined when the file sys-
tem is created. If this is not defined, the default time
applies.).
space Conserves space.
time Minimizes access time
You should generally optimize for shorter access times, unless the
file system is over 90% full.
SEE ALSO
mkfs(1M), newfs(1M), fork(2), terminfo(4).
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