no "defrag" in Linux?

[Paul Puschmann]

Peter Garrett <peter.garrett at optusnet.com.au> schrieb am Fri, Jul 21, 2006 at 02:31:56PM +1000:
> 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

Perhaps your files is now located on the outer areas of your harddisk
where the datarate is lower. But this is only speculation.

It could also be that there were some other process running, like
slocate / updatedb or whatever.

Paul
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