TUNEFS(8) TUNEFS(8) NAME tunefs - tune up an existing file system SYNOPSIS /etc/tunefs _t_u_n_e_u_p_-_o_p_t_i_o_n_s _s_p_e_c_i_a_l|_f_i_l_e_s_y_s DESCRIPTION _T_u_n_e_f_s is designed to change the dynamic parameters of a file system which affect the layout policies. The parameters which are to be changed are indicated by the flags given below: -a maxcontig This specifies the maximum number of contiguous blocks that will be laid out before forcing a rotational delay (see -d below). The default value is one, since most device drivers require an interrupt per disk transfer. Device drivers that can chain sev‐ eral buffers together in a single transfer should set this to the maximum chain length. -d rotdelay This specifies 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 maxbpg This indicates 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 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 cylinder group before seeking else‐ where. For file systems with exclusively large files, this parameter should be set higher. -m minfree This value specifies the percentage of space held back from nor‐ mal 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 allo‐ cating blocks, or it can attempt minimize the space fragmenta‐ tion 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. SEE ALSO fs(5), newfs(8), mkfs(8) M. McKusick, W. Joy, S. Leffler, R. Fabry, ‘‘A Fast File System for UNIX’’, _A_C_M _T_r_a_n_s_a_c_t_i_o_n_s _o_n _C_o_m_p_u_t_e_r _S_y_s_t_e_m_s _2, 3. pp 181-197, August 1984. (reprinted in the System Manager’s Manual, SMM:14) BUGS This program should work on mounted and active file systems. Because the super-block is not kept in the buffer cache, the changes will only take effect if the program is run on dismounted file systems. To change the root file system, the system must be rebooted after the file system is tuned. You can tune a file system, but you can’t tune a fish. 4.2 Berkeley Distribution May 22, 1986 TUNEFS(8)