tunefs(1M) tunefs(1M)NAME tunefs - tune an unmounted Berkeley 4.2 file system (UFS) SYNOPSIS /etc/tunefs [-p] [-mminfree] [-drotdelay] [-emaxbpg] [-amaxcontig] [-ooptimization] special DESCRIPTION tunefs either prints the value of or changes the dynamic parameters of a UFS file system that affects the layout pol- icies. FLAG OPTIONS -p Prints the current values of the maximum number of con- tiguous blocks, rotation delay, blocks per cylinder group, minimum free space, and optimization. The fol- lowing options are used to change these values: -mminfree Specify the percentage of space reserved from use by normal users. This value is the minimum free-space threshold. The default value of minfree is 10%. This value can be set to 0 for the file system, although up to a factor of three in throughput is 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 thres- hold. -drotdelay Specify the expected time (in milliseconds) to service a transfer-completion interrupt and initiate a new transfer on the same disk. The option is used to de- cide how much rotational spacing to place between suc- cessive blocks in a file. The value of rotdelay must be greater than or equal to 0 and less than or equal to 16. This value is set to 4 for the A/UX release dis- tribution of the root file system. -emaxbpg Specify 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 the value of maxbpg 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 degrad- ing 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 April, 1990 1
tunefs(1M) tunefs(1M)cylinder group before seeking elsewhere. For file sys- tems with exclusively large files, this parameter should be set higher. This value is set to 256 for the A/UX release distribution of the root file system. -amaxcontig Specify the maximum number of contiguous blocks that are laid out before forcing a rotational delay (see -d below). The default value is 1 because most device drivers require an interrupt per disk transfer. The value of maxcontig must be greater than 0 and less than or equal to 200. This value is set to 1 for the A/UX release distribution of the root file system. -ooptimization Specify that the file system can either try to minimize the time spent allocating blocks or can attempt to minimize the space fragmentation on the disk. If the value of minfree (see above) is less than 10%, 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. This value is set to time for the A/UX release distribution of the root file system. SEE ALSO fs(4), newfs(1M). BUGS This program should work on mounted and active file systems. Because the superblock is not kept in the buffer cache, the changes only take effect if the program is run on unmounted file systems. To change the root file system, the system must be rebooted after the file system is tuned. NOTES Device drivers that can chain several buffers together in a single transfer should set maxcontig to the maximum chain length. 2 April, 1990