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    1: .\"	$NetBSD: tunefs.8,v 1.1 2011/06/04 21:05:08 schmonz Exp $
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   30: .\"     @(#)tunefs.8	8.3 (Berkeley) 5/3/95
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   32: .Dd April 26, 2004
   33: .Dt TUNEFS 8
   34: .Os
   35: .Sh NAME
   36: .Nm tunefs
   37: .Nd tune up an existing file system
   38: .Sh SYNOPSIS
   39: .Nm
   40: .Op Fl AFN
   41: .Op Fl e Ar maxbpg
   42: .Op Fl g Ar avgfilesize
   43: .Op Fl h Ar avgfpdir
   44: .Op Fl l Ar logsize
   45: .Op Fl m Ar minfree
   46: .Bk -words
   47: .Op Fl o Ar optimize_preference
   48: .Ek
   49: .Ar special | Ar filesys
   50: .Sh DESCRIPTION
   51: .Nm
   52: is designed to change the dynamic parameters of a file system
   53: which affect the layout policies.
   54: .Pp
   55: The following options are supported by
   56: .Nm :
   57: .Bl -tag -width Ds
   58: .It Fl A
   59: Cause the values to be updated in all the alternate
   60: superblocks instead of just the standard superblock.
   61: If this option is not used,
   62: then use of a backup superblock by
   63: .Xr fsck 8
   64: will lose anything changed by
   65: .Nm .
   66: .Fl A
   67: is ignored when
   68: .Fl N
   69: is specified.
   70: .It Fl F
   71: Indicates that
   72: .Ar special
   73: is a file system image, rather than a device name or file system mount point.
   74: .Ar special
   75: will be accessed
   76: .Sq as-is .
   77: .It Fl N
   78: Display all the settable options
   79: (after any changes from the tuning options)
   80: but do not cause any of them to be changed.
   81: .It Fl e Ar maxbpg
   82: This indicates the maximum number of blocks any single file can
   83: allocate out of a cylinder group before it is forced to begin
   84: allocating blocks from another cylinder group.
   85: Typically this value is set to about one quarter of the total blocks
   86: in a cylinder group.
   87: The intent is to prevent any single file from using up all the
   88: blocks in a single cylinder group,
   89: thus degrading access times for all files subsequently allocated
   90: in that cylinder group.
   91: The effect of this limit is to cause big files to do long seeks
   92: more frequently than if they were allowed to allocate all the blocks
   93: in a cylinder group before seeking elsewhere.
   94: For file systems with exclusively large files,
   95: this parameter should be set higher.
   96: .It Fl g Ar avgfilesize
   97: This specifies the expected average file size.
   98: .It Fl h Ar avgfpdir
   99: This specifies the expected number of files per directory.
  100: .It Fl l Ar logsize
  101: This value specifies the size of the in-filesystem journaling log file.
  102: The default journaling log file size is described in
  103: .Xr wapbl 4 .
  104: Specifying a size of zero will cause the in-filesystem journaling log file
  105: to be removed the next time the filesystem is mounted.
  106: The size of an existing in-filesystem journaling log file can not be changed.
  107: .It Fl m Ar minfree
  108: This value specifies the percentage of space held back
  109: from normal users; the minimum free space threshold.
  110: The default value is set during creation of the filesystem, see
  111: .Xr newfs 8 .
  112: This value can be set to zero, however up to a factor of three
  113: in throughput will be lost over the performance obtained at a 5%
  114: threshold.
  115: Note that if the value is raised above the current usage level,
  116: users will be unable to allocate files until enough files have
  117: been deleted to get under the higher threshold.
  118: .It Fl o Ar optimize_preference
  119: The file system can either try to minimize the time spent
  120: allocating blocks, or it can attempt to minimize the space
  121: fragmentation on the disk.
  122: If the value of minfree (see above) is less than 5%,
  123: then the file system should optimize for space to avoid
  124: running out of full sized blocks.
  125: For values of minfree greater than or equal to 5%,
  126: fragmentation is unlikely to be problematical, and
  127: the file system can be optimized for time.
  128: .Pp
  129: .Ar optimize_preference
  130: can be specified as either
  131: .Li space
  132: or
  133: .Li time .
  134: .El
  135: .Sh SEE ALSO
  136: .Xr wapbl 4 ,
  137: .Xr fs 5 ,
  138: .Xr dumpfs 8 ,
  139: .Xr fsck_ffs 8 ,
  140: .Xr newfs 8
  141: .Rs
  142: .%A M. McKusick
  143: .%A W. Joy
  144: .%A S. Leffler
  145: .%A R. Fabry
  146: .%T "A Fast File System for UNIX"
  147: .%J "ACM Transactions on Computer Systems 2"
  148: .%N 3
  149: .%P pp 181-197
  150: .%D August 1984
  151: .%O "(reprinted in the BSD System Manager's Manual, SMM:5)"
  152: .Re
  153: .Sh HISTORY
  154: The
  155: .Nm
  156: command appeared in
  157: .Bx 4.2 .
  158: .Sh BUGS
  159: This program should work on mounted and active file systems.
  160: Because the super-block is not kept in the buffer cache,
  161: the changes will only take effect if the program
  162: is run on unmounted file systems.
  163: To change the root file system, the system must be rebooted
  164: after the file system is tuned.
  165: .Pp
  166: .\" Take this out and a Unix Demon will dog your steps from now until
  167: .\" the time_t's wrap around.
  168: You can tune a file system, but you can't tune a fish.