'\"macro stdmacro
.if n .pH g1a.tunefs @(#)tunefs	40.10 of 1/17/90
.\" Copyright 1989 AT&T
.nr X
.if \nX=0 .ds x} tunefs 1M "UFS" "\&"
.if \nX=1 .ds x} tunefs 1M "UFS"
.if \nX=2 .ds x} tunefs 1M "" "\&"
.if \nX=3 .ds x} tunefs "" "" "\&"
.TH \*(x}
.SH NAME
\f4tunefs\f1 \- tune up an existing file system
.SH SYNOPSIS
\f4tunefs\f1
[\f4\-a\f2 maxcontig\f1]
[\f4\-d\f2 rotdelay\f1]
[\f4\-e\f2 maxbpg\f1]
[\f4\-m\f2 minfree\f1]
[\f4-o [s | t]\fP]
.IR special\  |\  filesystem
.SH DESCRIPTION
.LP
\f4tunefs\f1
is designed to change the dynamic parameters
of a file system which affect the layout policies.
The file system must be unmounted before using \f4tunefs\f1.
The parameters which are to be changed are indicated
by the options given below:
.LP
The options are:
.TP .85i
\f4\-a\f2 maxcontig\f1
Specify the maximum number of contiguous
blocks that will be laid out before forcing
a rotational delay (see
\f4\-d\f1
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.
.TP
\f4\-d\f2 rotdelay\f1
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.
.TP
\f4\-e\f2 maxbpg\f1
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.
.TP
\f4\-m\f2 minfree\f1
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.
.TP
\f4-o [s | t]\fP
Change optimization strategy for the file system.
.sp .5
\f4s\fP - space (conserve space)
.br
\f4t\fP - time (attempt to organize file layout to minimize access time.
.P
Generally one should optimize for time unless the file system
is over 90% full.
.SH "SEE ALSO"
\f4mkfs\fP(1M), \f4ufs\fP(4).
\f4fork\f1(2), \f4terminfo\f1(4)
in the \f2Programmer's Reference Manual\f1.
