Apple provides a handy application for working with hard drives called Disk Utility. If you open Disk Utility, you’ll notice that it doesn’t include a tool to defragment any of the drives connected to your Mac. The reason for this perception is that a Mac running any version of OS X after 10.2 doesn’t need to be defragmented. OS X, as well as macOS, have their own built-in safeguards that prevent files from becoming fragmented in the first place.
- The Mac’s HFS+ file system tries not to use newly freed file space on a disk. Instead, it searches for larger free areas already present on the drive, thus avoiding fragmenting files just to fit them into the available space.
- Mac OS dynamically gathers groups of small files and combines them into larger areas of the disk automatically. The process of writing the files to a new, larger location defragments all the files in the group.
- OS X and MacOS implement Hot File Adaptive Clustering, which monitors frequently accessed files that are not modified (read-only), and then moves these frequently accessed files to a special hot zone on the startup drive. In the process of moving these files, OS X defragments them and then stores them in the area of the drive that has the fastest access.
- When you open a file, your Mac checks to see if it’s highly fragmented (more than 8 fragments). If so, the operating system will automatically defragment the file.
The result of all these security measures is that the Mac rarely, if ever, needs its disk space to be defragmented. The only real exception to this is when your hard drive has less than 10 percent free space. At this point, the Mac operating system is unable to perform its automatic defragmentation routines, so you should consider deleting files or expanding the size of your disk storage.
Is there a reason I shouldn’t defrag my Mac’s drive?
As we mentioned earlier, you probably don’t need to defragment your drives, because your Mac takes care of that for you. However, there are some types of tasks that can benefit from defragmented drives; specifically, when working with real-time or near real-time data acquisition or manipulation. Think about recording and editing video or audio, acquiring complex scientific data, or working with time-sensitive data.
This only applies to standard hard drives. If you’re using an SSD or Fusion Drive, your data should never be defragmented, as doing so can cause write amplification, a common cause of premature SSD failure. SSDs have a finite number of writes that can be performed. You can think of it as the memory location inside the SSD becoming brittle with age. Each write to a memory location increases the age of the cell.
Because flash-based storage requires memory locations to be erased before new data can be written to them, the process of defragmenting an SSD can cause multiple write cycles, causing excessive wear on memory. the SSD drive.
Will defragmenting damage my drive?
As we’ve mentioned, defragmenting an SSD or any flash-based storage device (this includes Fusion-based drives that use a small SSD/flash device along with a standard hard drive) can cause premature failure by increasing the amount of wear (writing and reading of the storage cells). In the case of a hard drive, which uses a mechanical spinning disk, there is no significant chance of damaging the hard drive, or your Mac, simply by performing a defragmentation. The only negative comes in the time it takes to perform the defragmentation.
What if I decide I need to defrag?
There are third-party utilities available that can defrag your Mac’s drives. One of our favorites for this task is Drive Genius 4.
Drive Genius 4 does much more than offer the ability to defragment a Mac’s drive; includes the ability to monitor drive status and repair most drive problems.