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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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