tunefs —
tune up an existing file system
  
    | tunefs | [ -AFN] [-emaxbpg] [-gavgfilesize] [-havgfpdir] [-llogsize] [-mminfree] [-ooptimize_preference] [-qquota] [-Ssectorsize] special |
      filesys | 
tunefs is designed to change the dynamic parameters of a
  file system which affect the layout policies.
The following options are supported by
    tunefs:
  - -A
- Cause the values to be updated in all the alternate superblocks instead of
      just the standard superblock. If this option is not used, then use of a
      backup superblock by fsck(8)
      will lose anything changed by tunefs.-Ais ignored when-Nis
      specified.
- -F
- Indicates that special is a file system image,
      rather than a device name or file system mount point.
      special will be accessed ‘as-is’.
- -N
- Display all the settable options (after any changes from the tuning
      options) but do not cause any of them to be changed.
- -emaxbpg
- 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 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.
- -gavgfilesize
- This specifies the expected average file size.
- -havgfpdir
- This specifies the expected number of files per directory.
- -llogsize
- This value specifies the size of the in-filesystem journaling log file.
      The default journaling log file size is described in
      wapbl(4). Specifying a size
      of zero will cause the in-filesystem journaling log file to be removed the
      next time the filesystem is mounted. The size of an existing in-filesystem
      journaling log file can not be changed directly. You need to first set the
      log file size to zero, then mount the filesystem without logging enabled
      (which will remove the log without creating a new one), unmount, set the
      size to the new value and finally re-mount with logging enabled.
- -mminfree
- This value specifies the percentage of space held back from normal users;
      the minimum free space threshold. The default value is set during creation
      of the filesystem, see
      newfs(8). 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 5% 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.
- -ooptimize_preference
- The file system can either try to minimize the time spent allocating
      blocks, or it can attempt to minimize the space fragmentation on the disk.
      If the value of minfree (see above) is less than 5%, 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 5%, fragmentation is unlikely
      to be problematical, and the file system can be optimized for time.
    optimize_preference can be specified as
        either spaceortime.
 
- -qquota
- enable or disable a quota. quota can be one of
      user,group,nouserornogroupto
      enable or disable the specified quota type. Multiple-qcan be used to enable/disable all types at
      once.After enabling a quota,
        fsck_ffs(8) has to be
        run to compute the correct quota values. 
- -Ssectorsize
- changes the fsbtodb value in the superblock to reflect a particular
      physical sector size. This value is ignored by the
      NetBSD kernel but needed by tools like
      fsck_ffs(8) to access disk
      blocks correctly. The minimum value is DEV_BSIZE(512).Changing the fsbtodb value becomes necessary when a filesystem
        image is created for one sector size and then transferred to a device
        with a different sector size and should be applied also to the alternate
        superblocks. 
wapbl(4),
  fs(5),
  dumpfs(8),
  fsck_ffs(8),
  newfs(8)M. McKusick,
    W. Joy, S. Leffler, and
    R. Fabry, A Fast File System for
    UNIX, ACM Transactions on Computer Systems 2,
    3, pp 181-197,
    August 1984, (reprinted in the
    BSD System Manager's Manual, SMM:5).
The tunefs command appeared in
  4.2BSD.
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 unmounted 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.