OSF

NAME

tunefs − Tune up an existing UFS file system

SYNOPSIS

tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree] [-o optimization_preference] file_system

FLAGS

-a maxcontigSepcifies the maximum number of contiguous blocks that will be laid out before forcing a rotational delay (see the −d flag).  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. 

-d rotdelaySpecifies 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. 

-e maxbpgIndicates 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 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. 

-m minfreeSpecifies 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 that 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 optimization_preference
The file system can either try to minimize the time spent allocating blocks, or it can attempt minimize the space fragmentation on the disk. If the value of minfree (see above) is less than 10%, then the file system should optimize for space to avoid running out of full sized blocks.  For values of minfree greater than or equal to 10%, fragmentation is unlikely to be problematical, and the file system can be optimized for time. 

DESCRIPTION

The tunefs command changes the dynamic parameters of a UFS file system which affect the layout policies.  The parameters which are to be changed are indicated by the flags specified. 

This program should work on mounted and active file systems.  Because the superblock is not kept in the buffer cache, the changes will only take effect if the program is run on unmounted file systems. 

The system must be rebooted after the root file system is tuned.  You must be root to use this command. 

FILES

/usr/sbin/tunefs
Specifies the command path

RELATED INFORMATION

Commands:  newfs(8)