OS X Defragment

OS X has its own built-in safeguards that prevent files from becoming fragmented in the first place.

* HFS+ file system in Mac doesn't use recently freed file space on a Mac disk. Instead, it looks for larger free areas already present on the drive, thereby avoiding fragmenting files just to fit them into available space.
* OS X dynamically gathers groups of small files and combines them into larger areas on your disk automatically. The process of writing the files to a new larger location defragments all of the files in the group.
* OS X implements Hot File Adaptive Clustering, which monitors frequently-accessed files that do not get changed (read only), and then moves these often-accessed files to a special hot zone on the hard drive. In the process of moving these files, OS X defragments them, and then stores them in the area of the hard drive that has the fastest access.
* When you open a file, OS X checks to see if it is highly fragmented (more than 8 fragments). If it is, OS X will automatically defragment the file.

The result of all these safeguards is that OSX rarely, if ever, needs to have its disk space defragmented. The only real exception to this is when your hard drive has less than 10 percent free space. At that point, OS X is unable to perform its automatic defragmentation routines, and you should consider either removing files or go for some third party defragmenting tool for Mac.

Its also important to note that although the Mac OS X is too smart to handle the fragmented files but its limited to 20 MB only. If a user want to defrag a file larger than 20 MB, he must use a third party Mac Defragger.