OS X Defragmentation

[Will Jones]

Due to Mac OS X's File System, Defragmentation is only necessary if you have less than 20% of your drive free. If that is the case, you may notice a slight improvement in performance when your Hard Drive is defragmented. To do this, you will need to purchase a product such as PlusOptimizer from Alsoft Inc. (bundled with DiskWarrior).
(http://www.ambitiouslemon.com/hints.php?id=28)

Can someone explain to me what it is about OS X's file structure that results in only having to defrag when your harddrive is using 80% (or more) of it's total capacity?

Thanks,
Will

PS. Apologies if this has been covered before, which it most probably has somewhere along the line.

[benixau]

yeah as any less and you are wasting time as OS X scatters swap files all over the place. at 20% free they are in such a small space that they are pretty much going to be ignored by a defrag app.

long:

the swap file will be in the 20% free and the defrag app will treat them as a file to be placed at the end of the file system. Therefore the rest of your file system will be concatenated properly. At more than 20% free the swap will more liekly be treated as a permanent file and placed around the middle meaning that when OS X deletes it you have free space in the middle of your HDD. As soon as a file is written to your HDD it will go into the first free space which happens to be in the middle instead of the end, i.e. the free space is no longer concatenated.

hope it helps. :)

[mac15]

Defragmentation isn't really a necesstiy, plus it takes almost 24 hours to defrag my HD, 40 gigger, 30gig full. It didn't speed it up all that much, but if your really picky, then by all means do it.