Disk Fragmentation

In the old days spinning hard disks getting fragmented was a real problem. It slowed down your HD quite a bit, so tech people would “defragment” their hard drives periodically. One app on the Mac that can do that is Drive Genius by Prosoft Engineering. What is fragmentation you ask?



Hard drive fragmentation occurs when various parts of a file are place in different sectors of the hard drive. So, when you open that file the HD has to go assemble all these parts and then it opens. If the parts are all over the place it can slow down the HD a bit. Over a period of time fragmentation increases and the HD slows down more and more. The “defrag” process collects all those file pieces and puts them all together again on the HD so the file is accessed more quickly. That is the theory anyway. Need to mention a couple of things here though.

First, OS X is supposed to handle defragmentation on it’s own, in the OS. So, “defragging” a OS X drive is unnecessary they tell us. I suppose we need to take that at face value.

Second, defraging a HD can be dangerous. Case in point I defragged my iMac Fusion HD a few years back and it hosed the operating system, had to reinstall it. Of course, a Fusion drive is part SSD and part spinner so that may be a problem.

So, what to do? I have El Capitan Beta running on an external spinning HD in it’s own partition. I knew about the fragmentation because Drive Genius’s Drive Pulse feature that monitors all the HD’s on your system gave me a fragmentation warning. That is what got me into the fragmentation thing in the first place. I decided to defrag the beta drive. Hey, if it messes up, I can always reinstall the beta right?

Drive Genius Defrag

When you go into the Drive Genius app area you will see this window. In this case the El Capitan drive was a partition of another drive. You have to select the physical drive in question in the sidebar, then go to the dropdown menu and select the partition:

Once you select the drive partition just click on the Defragment icon and away you go. I mentioned that defragging can be dangerous. Before starting the defrag processes Drive Genius gives you a warning like so:

Once you click the “Start” button you will see this screen:

Defragging your HD can take a long time. This partition is only about 90 GB, so it only took about an hour, but if you are doing a large drive or partition I would recommend doing it overnight.

When the process is finished you should see a window like this:

After defragging my El Capitan Beta partition I booted into it. All appeared to be fine. It did seem like the apps booted a smidgen faster. But, all the apps seemed to work properly.

Please note that all the research I could find online indicated that defragging a SSD type drive is unnecessary due to the way it stores and feeds files. Also, you cannot defrag the boot drive on your Mac you have to have what Prosoft calls a “Bootwell” thumb drive or an external Tech Drive like I have to boot onto to defrag the main startup drive on your Mac.


Should you defrag your spinning HD? I really don’t know for sure. It appears that OS X does a fairly decent job of managing files. I guess I would say that the advantages in speed increase on the drive would be moderate. It may be worth your while if you have been using a drive for a really long time and it seems to be bogging down a bit. As usual, having a good backup on hand is crucial for any type of procedure like this.