tunefs(1M)

NAME

tunefs − tune up an existing file system

SYNOPSIS

/etc/tunefs tuneup-options special

DESCRIPTION

tunefs is used to change a file system’s dynamic parameters that affect the layout policies. Parameters that are to be changed are specified by the flags given below:

−a maxcontig Set the maximum number of contiguous blocks that will be laid out before forcing a rotational delay to maxcotig (see −d below). The default value is 1, because most device drivers require one interrupt per disk transfer. For device drivers that can chain several buffers together in a single transfer, set maxcontig to the maximum chain length.

−d rotdelay rotdelay is the expected time (in milliseconds) to service a transfer completion interrupt and initiate a new transfer on the same disk. It is used to determine how much rotational spacing to place between successive blocks in a file.

−e maxbpg maxbpg specifies 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 about one fourth 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 large 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 minfree specifies the percentage of space that is not available to normal users; i.e., the minimum free space threshold. The default value used is 10%. This value can be set to zero. If it is, throughput performance degrades by as much as 3 to 1 in comparison with a 10% threshold. Note that if minfree is raised above the current usage level, users will be unable to allocate files until enough files have been deleted to meet the new threshold requirement.

−v Current values contained in the primary superblock are displayed to standard output.

−A Redundant super-blocks as well as the super-block are to be modified as indicated above.

special special is the name of the file system to be tuned. It is either a block or character special file for an unmounted volume or volume section.

WARNINGS

This program should work on mounted and active file systems. Because the super-block is not kept in the buffer cache, tunefs takes effect only if it is run on unmounted file systems. If run on the root file system, the system must be rebooted.

You can tune a file system, but you can’t tune a fish.

AUTHOR

tunefs was developed by the University of California, Berkeley.

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