Installing programs, browsing the Internet and tinkering with various applications can cause all computer operating systems including the Mac to eventually get cluttered with junk files that eat up space and cause the hard drive to become sluggish. This is called fragmenting or fragmentation.
Fragmentation also occurs when files are created and deleted. If you create and delete large amounts of files, the hard drive may become so fragmented you start noticing that it is slowing down of file system performance. For example, you create three files, and then decide to delete the second one.
You then save a fourth file that is larger than the second one. The computer file system may put a portion of the fourth file in the space that was occupied by the second and the remainder of that file after the third file. In able to access the entire file, the system has to look in two places.
The file system used on Macintosh computers is designed to work with a certain degree of fragmentation. This is normal and does not affect the performance for majority of users. However, the nature of the work you are doing, random-access disk mechanisms, and the exact order in which the files are segmented can all have a bearing on performance.
If your disks are almost full, and you often modify or create large files, such as editing video, there is a chance the disks could be fragmented.
According to Apple the Mac operating system does not need to be de-fragmented. After installing system updates or new applications, the system will optimize itself. Here’s why, they supply an application for working with hard drives called Disk Utility but, if you open it, you will notice that it does not include a tool for de-fragmenting your hard drive as on other operating systems.
The reason for this perceived oversight is that a Mac running any version of OS X later than 10.2 does not need to be de-fragmented. OS X has its own built-in safeguards that prevent files from becoming fragmented in the first place.
Hard disk capacity is much greater now than a few years ago and with more free space available, the file system does not need to fill every “nook and cranny”. The Mac OS eliminates reusing space from the deleted files as much as possible, which in turn avoids filling small areas of recently-freed space therefore, when you open a file, Mac OS X checks to see if it is highly fragmented (more than 8 fragments). If it is, OS X will automatically de-fragment the file.
If you still think you need to de-fragment, try restarting your computer first. It might help, Mac OS and it’s easy to do. You can also clone your drive to an external disk, erase your internal disk, then clone back your files; this will effectively de-frag your disk.
At this point, if you are still having problems, you can either use third-party de-fragmenting software or back up your hard disk and use the Apple Drive Setup disk to reinitialize or restore your files.
WARNING: using the Apple Drive Setup disk to reinitialize will erase all the files on your hard disk. Make sure you have a complete backup, so you will be able to restore all your files once the initialization is complete.
The de-fragmenting process generally causes a large amount of disk activity due to the volume of data being rearranged. This can take several hours to complete, so if you decide to use third-party de-fragmenting software, I suggest running it when you plan on being off the computer for several hours, preferably overnight.
Adir Mashiach is a computer expert since 2003. He runs a website called Defrag Your Computer that aims to help people to solve their problem having a slow mac because of the cluttered hard drive. In his website you can find more information about defrag Mac.