This link contains a lot of ignorant nonsense.
Further to this, it defragments sufficiently large files when you open them if it considers that there is sufficiently much free space that it can afford to do a defragment without temporarily consuming bytes you may be relying on being available.It defragments files smaller than 20MB. It doesn't defragment the whole drive, which means free space can fragment up. iDefrag is a program that can defrag HFS drives.
You wouldn't and shouldn't defragment an SSD.With the "is a defrag needed on OS X" aside...
How would defrag on a conventional disk differ from defrag on a solid state drive?
Nope, only files up to 20MB.Further to this, it defragments sufficiently large files when you open them if it considers that there is sufficiently much free space that it can afford to do a defragment without temporarily consuming bytes you may be relying on being available.
The free-space rule applies to every OS with intelligent placement algorithms, which is all of them these days....users should keep at least 10% of disk space free for optimal performance.
HFS is a B-tree based system, and the only way the B-trees get cleaned up is with a full defrag. If Defrag didn't have such an impact, you wouldn't see such a fascination with 'clean installs' of OSX.Given the various conditions applied, it is not unlikely that a program like iDefrag will be able to find files that exist in multiple fragments and to correct the fragmentation and for the whole process to have no effect on system performance.