no "defrag" in Linux?

[Peter Garrett]

On Thu, 20 Jul 2006 15:34:47 -0700
"Henk Postma" <henkpm at gmail.com> wrote:
[snip]
> Go ahead and try the following.
> 1) locate a large file (divx movie?).
> 2) sudo filefrag $movie, note the level of fragmentation
> 3) time cat $movie > /dev/null, note the time it took
> 4) now make a copy of the movie:
> cp $movie $movie.new
> 5) sudo filefrag $movie.new Most likely, you will find that it is less
> fragmented
> 6) time cat $movie.new > /dev/null
> 
> I guarantee you will see a big reduction in time it takes to dump the
> file to /dev/null

Tried it on the "Elephant's Dream" movie ( ED_1024.avi)

 $ du -h ED_1024.avi
426M    ED_1024.avi

$ sudo filefrag ED_1024.avi
ED_1024.avi: 294 extents found, perfection would be 4 extents

$ time cat ED_1024.avi > /dev/null

real    0m11.178s
user    0m0.052s
sys     0m1.056s

$ cp ED_1024.avi ED_1024-new.avi
$ sudo filefrag ED_1024-new.avi
ED_1024-new.avi: 103 extents found, perfection would be 4 extents

$ time cat ED_1024-new.avi > /dev/null

real    0m11.470s
user    0m0.060s
sys     0m1.156s

OK, it seems to be less fragmented, but if anything it takes *longer* to
cat it to /dev/null  ( or about the same - although doing it several
times, each time the new file took longer)

Did I miss something ? 

Peter