TUNEFS(1M) Maintenance Commands TUNEFS(1M)


tunefs - tune an existing UFS file system


tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg]
[-m minfree] [-o space | time] special | filesystem


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.


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This parameter is obsolete as of the Solaris 10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

-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.


See largefile(5) for the description of the behavior of tunefs when
encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).


mkfs_ufs(1M), newfs(1M), attributes(5), largefile(5)

December 5, 2003 TUNEFS(1M)