4.4BSD/usr/share/man/cat8/tunefs.0

TUNEFS(8)                 BSD System Manager's Manual                TUNEFS(8)

NNAAMMEE
     ttuunneeffss - tune up an existing file system

SSYYNNOOPPSSIISS
     ttuunneeffss [--aa _m_a_x_c_o_n_t_i_g] [--dd _r_o_t_d_e_l_a_y] [--ee _m_a_x_b_p_g] [--mm _m_i_n_f_r_e_e]
            [--oo _o_p_t_i_m_i_z_e___p_r_e_f_e_r_e_n_c_e] [_s_p_e_c_i_a_l | _f_i_l_e_s_y_s]

DDEESSCCRRIIPPTTIIOONN
     TTuunneeffss 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:

     --aa _m_a_x_c_o_n_t_i_g
             This specifies the maximum number of contiguous blocks that will
             be laid out before forcing a rotational delay (see --dd 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.

     --dd _r_o_t_d_e_l_a_y
             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.

     --ee _m_a_x_b_p_g
             This indicates the maximum number of blocks any single file can
             allocate out of a cylinder group before it is forced to begin al-
             locating blocks from another cylinder group.  Typically this val-
             ue 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.

     --mm _m_i_n_f_r_e_e
             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 fac-
             tor of three in throughput will be lost over the performance ob-
             tained 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 high-
             er threshold.

     --oo _o_p_t_i_m_i_z_e___p_r_e_f_e_r_e_n_c_e
             The file system can either try to minimize the time spent allo-
             cating 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 run-
             ning out of full sized blocks.  For values of minfree greater
             than or equal to 10%, fragmentation is unlikely to be problemati-
             cal, and the file system can be optimized for time.

SSEEEE AALLSSOO
     fs(5),  dumpfs(8),  newfs(8),  mkfs(8)


     M. McKusick, W. Joy, S. Leffler, and 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 BSD System Manager's Manual, SMM:5).

BBUUGGSS
     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.

HHIISSTTOORRYY
     The ttuunneeffss command appeared in 4.2BSD.

4.2 Berkeley Distribution        June 5, 1993                                2