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1.1     ! root        1: .TH TUNEFS 8 "20 February 1983"
        !             2: .UC 4
        !             3: .SH NAME
        !             4: tunefs \- tune up an existing file system
        !             5: .SH SYNOPSIS
        !             6: .B /etc/tunefs
        !             7: .I tuneup-options
        !             8: .IR special | filesys
        !             9: .SH DESCRIPTION
        !            10: .I Tunefs
        !            11: is designed to change the dynamic parameters of a file system
        !            12: which affect the layout policies.
        !            13: The parameters which are to be changed are indicated by the flags
        !            14: given below:
        !            15: .IP "\fB\-a\fP maxcontig"
        !            16: .br
        !            17: This specifies the maximum number of contiguous blocks that will
        !            18: be laid out before forcing a rotational delay (see \-d below).
        !            19: The default value is one, since most device drivers require
        !            20: an interrupt per disk transfer.
        !            21: Device drivers that can chain several buffers together in a single
        !            22: transfer should set this to the maximum chain length.
        !            23: .IP "\fB\-d\fP rotdelay"
        !            24: .br
        !            25: This specifies the expected time (in milliseconds)
        !            26: to service a transfer completion
        !            27: interrupt and initiate a new transfer on the same disk.
        !            28: It is used to decide how much rotational spacing to place between
        !            29: successive blocks in a file.
        !            30: .IP "\fB\-e\fP maxbpg"
        !            31: .br
        !            32: This indicates the maximum number of blocks any single file can
        !            33: allocate out of a cylinder group before it is forced to begin
        !            34: allocating blocks from another cylinder group.
        !            35: Typically this value is set to about one quarter of the total blocks
        !            36: in a cylinder group.
        !            37: The intent is to prevent any single file from using up all the
        !            38: blocks in a single cylinder group,
        !            39: thus degrading access times for all files subsequently allocated 
        !            40: in that cylinder group.
        !            41: The effect of this limit is to cause big files to do long seeks
        !            42: more frequently than if they were allowed to allocate all the blocks
        !            43: in a cylinder group before seeking elsewhere.
        !            44: For file systems with exclusively large files, 
        !            45: this parameter should be set higher.
        !            46: .IP "\fB\-m\fP minfree"
        !            47: .br
        !            48: This value specifies the percentage of space held back
        !            49: from normal users; the minimum free space threshold.
        !            50: The default value used is 10%.
        !            51: This value can be set to zero, however up to a factor of three
        !            52: in throughput will be lost over the performance obtained at a 10%
        !            53: threshold.
        !            54: Note that if the value is raised above the current usage level,
        !            55: users will be unable to allocate files until enough files have
        !            56: been deleted to get under the higher threshold.
        !            57: .SH "SEE ALSO"
        !            58: fs(5),
        !            59: newfs(8),
        !            60: mkfs(8)
        !            61: .PP
        !            62: McKusick, Joy, Leffler; "A Fast File System for Unix",
        !            63: Computer Systems Research Group, Dept of EECS, Berkeley, CA 94720;
        !            64: TR #7, September 1982.
        !            65: .SH BUGS
        !            66: This program should work on mounted and active file systems.
        !            67: Because the super-block is not kept in the buffer cache,
        !            68: the program will only take effect if it is run on dismounted file systems.
        !            69: (if run on the root file system, the system must be rebooted)
        !            70: .PP
        !            71: You can tune a file system, but you can't tune a fish.

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