fmap -- Command

Measure fragmentation of the free list
fmap device

Command fmap tests how fragmented the  free list is on COHERENT file system
device. It briefly displays its results  and returns an exit status that is
equivalent to the percent of fragmentation found on device.

You can use the amount of  fragmentation of the free list to decide whether
to  de-fragment device.  When the  freelist is  fragmented, writing  a file
creates a file that is not  physically contiguous; and this, in turn, slows
disk I/O.

device must be  a partition on your hard disk  or a floppy disk rather than
an entire hard  drive.  It can be either the  raw or the ``cooked'' (block)
device.  For example, the command

    fmap /dev/rat0a

tells fmap to map the free list on the first partition on the first drive.

Because fmap  returns an exit  status equal to  the integer portion  of the
percentage of  fragmentation found,  you can  use it in  a shell  script to
alert the  system administrator when the file  system needs attention.  For
example, the  following shell script  tests the level  of  fragmentation on
the device given as an argument;  if the fragmentation exceeds 5%, it sends
mail to the superuser root:

fmap /dev/$1
a=$?
if expr $a gt; 5
then
    echo  -n "fmap of " >/tmp/rootmail
    echo -n $1 >>/tmp/rootmail
    echo -n " shows " >>/tmp/rootmail
    echo -n $a >>/tmp/rootmail
    echo " percent fragmentaion" >>/tmp/rootmail
    echo -n $a >>/tmp/rootmail
    echo " is greater than 5"  >>/tmp/rootmail
    echo -n "therefore, it is time to defrag " >>/tmp/rootmail
    echo $1 >>/tmp/rootmail
    echo "bye" >>/tmp/rootmail
    mail root </tmp/rootmail
    rm /tmp/rootmail
fi
exit 0

See Also

commands,
dpac,
fsck,
qpac,
upac

Notes

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

© 2012 by Stephen A. Ness