TUNEFS(8) Maintenance Commands and Procedures TUNEFS(8)

NAME

tunefs - tune 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
that affect the layout policies. When using tunefs with filesystem,
filesystem must be in /etc/vfstab. The parameters that can be changed
are indicated by the options given below.

OPTIONS

The following options are supported:

-a maxcontig
The maximum number of logical blocks, belonging
to one file, that is allocated contiguously. The
default is calculated as follows:

maxcontig = disk drive maximum transfer size / disk block size


If the disk drive's maximum transfer size cannot
be determined, the default value for maxcontig
is calculated from kernel parameters as follows:

If maxphys is less than ufs_maxmaxphys, which is
1 Mbyte, then maxcontig is set to maxphys.
Otherwise, maxcontig is set to ufs_maxmaxphys.

You can set maxcontig to any positive integer
value.

The actual value will be the lesser of what has
been specified and what the hardware supports.


-d rotdelay
This parameter is obsolete as of the Solaris 10
release. The value is always set to 0,
regardless of the input value.


-e maxbpg
Indicates the maximum number of contiguous
logical blocks any single file can allocate from
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 contiguous logical 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.


-m minfree
Specifies the minimum free space threshold, or
the percentage of space held back from normal
users. This value can be set to 0. 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.


-o space|time
The file system can either be instructed to try
to minimize the time spent allocating blocks, or
to try to minimize the space fragmentation on
the disk. The default is time.

Generally, you should optimize for time unless
the file system is over 90% full.

USAGE

See largefile(7) for the description of the behavior of tunefs when
encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

SEE ALSO

attributes(7), largefile(7), mkfs_ufs(8), newfs(8)

December 5, 2003 TUNEFS(8)