tunefs(1M) (man pages section 1M: System Administration Commands)

man pages section 1M: System Administration Commands

tunefs(1M)

NAME

tunefs– tune an existing UFS file system

SYNOPSIS

tunefs

-a

maxcontig

-d

rotdelay

-e

maxbpg

-m

minfree

-o

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This parameter is obsolete. 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(5) for the description of the behavior of tunefs when encountering files greater than or equal to 2 Gbyte ( 2³¹ bytes).

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Availability	SUNWcsu