dpac -- Command

De-fragment a COHERENT file system
dpac [-q] raw_device

Command  dpac   de-fragments  the  COHERENT  file   system  on  raw_device.
Defragmentation leaves each  file in the file system physically contiguous.
This reduces  the number  of seeks  needed to access  a file,  and threfore
permits disk I/O  to run at its maximum speed.   The default algorithm also
sorts the  i-nodes by  modification date  and puts the  oldest ones  at the
beginning  of  the  partition.   This  helps  the file  system  remain  un-
fragmented longer.

You must  umount the target file  system raw_device before you  run dpac on
it.   Failure to  do so  will corrupt  the file  system.  For  example, the
command

    dpac /dev/rat0a

tells dpac to map the first partition on the first drive and prompt whether
to continue.  raw_device  must be a partition or a  floppy disk rather than
an entire hard drive.

dpac begins by making a map of the file system.  It displays a histogram of
its activity as  it builds the map; this lets  you see what the kernel must
do in order to access each file.  When it has finished the file system map,
dpac prompts you and  asks whether to quit, continue with defragmentatation
using the default  date sort, or to continue but  to use an unsorted method
of defragmentation.  dpac does not use terminfo or termcap for its display,
and is  intended for  use on the  console's ansipc terminal  setting.  This
lets you run it from a bootable floppy disk.

See Also

commands,
fmap,
fsck,
qpac,
spac,
upac

Notes

To see how fragmented a file system is, use the command fmap.

Note that you  can also de-fragment a file system  by copying it to a tape,
then  deleting  it and  restoring  it  from the  tape.   Another method  of
defragmentation is  to use the command  cpdir to copy the  file system to a
spare partition (should you have one  that is large enough), then using the
spare partition in place of the old partition.

Please note that if you  use dpac incorrectly or without sufficient amounts
of RAM  or spare disk  space, you can  damage or destroy  your file system.
Never run  dpac on the partition-table device (e.g.,  /dev/at0x), or on the
root device.  Caveat utilitor!

dpac was written by Randy Wright (rw@rwsys.wimsey.bc.ca).

© 2012 by Stephen A. Ness