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

NAME

       tunefs - tune up an existing file system

SYNOPSIS

       tunefs tuneup-options special|filesys

DESCRIPTION

       Tunefs  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:

       -a maxcontig
	      This specifies the maximum number of contiguous blocks that will be laid out before forcing a rotational delay (see -d below).   The
	      default  value is one, since most device drivers require an interrupt per disk transfer.	Device drivers that can chain several buf-
	      fers together in a single transfer should set this to the maximum chain length.

       -d rotdelay
	      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.

       -e maxbpg
	      This  indicates the maximum number of blocks any single file can allocate out of a cylinder group before it is forced to begin allo-
	      cating 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.

       -m minfree
	      This value specifies the percentage of space held back from normal users; the minimum free space threshold.  The default value  used
	      is  10%.	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 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 higher threshold.

       -o optimization preference
	      The  file  system can either try to minimize the time spent allocating 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 running out
	      of  full	sized  blocks.	For values of minfree greater than or equal to 10%, fragmentation is unlikely to be problematical, and the
	      file system can be optimized for time.

SEE ALSO

       fs(5), newfs(8), mkfs(8)

       M. McKusick, W. Joy, S. Leffler, R. Fabry, ``A Fast File System for UNIX'', ACM Transactions on Computer Systems 2, 3.  pp 181-197,  August
       1984.  (reprinted in the System Manager's Manual, SMM:14)

BUGS

       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.

       tunefs is not currently implemented in 2.11BSD.

       You can tune a file system, but you can't tune a fish.

4.2 Berkeley Distribution					 November 17, 1996							 TUNEFS(8)