Fusion Drive Speedup

I usually keep an iMac 5-6 years. That is what works out best for me for my Speed vs. Storage needs. My Late 2012 iMac 27″ is still a viable machine, but it is slowing down a bit so I have started looking into ways to upgrade it. “I feel the need for speed” as one famous actor once opined.


My Setup

My iMac is using a Fusion Drive. It was the first Fusion Drive Apple produced, the SSD portion is 128 GB. The actual spinning hard drive is 1 TB. Yes, it is still pretty fast, but as I mentioned it seems to be slowing down some. Actually, it is running at the speeds it was designed for, it is just that OS X and many of the apps I use are becoming more sophisticated, larger and need more power to run. I did upgrade the RAM on the machine to 32 GB which has helped some.

I have been researching upgrading the SSD portion of the Fusion Drive to a newer, larger, faster SSD. This is very complicated. It includes removing everything including the Logic Board, the Fusion SSD is plugged into the bottom side of the Logic Board. However, in my travels I came across an article that suggested running First Aid in the Disk Utility app on the Fusion Drive would improve it’s performance.

Disk Utility

There is one caveat to performing this procedure on the Fusion Drive. You have to be booted from an external source. I have a Tech HD so I booted from the Tech HD and ran it from there. You may have OS X on a Thumb Drive that you can boot from. Theoretically (I did not test this) you should be able to boot your Mac in Recovery Mode (hold down the Command Key and the “R” key upon Restart) and then start Disk Utility from there. When finished just Reboot.

At any rate, once booted into an external source just open Disk Utility in the Utilities folder:

Once it is open select the “Fusion Drive” and then click on “First Aid”. You will get this dropdown:

Click “Run” and let it do it’s thing. It may be of interest to you to click on the “Details” button to see what it is checking and/or fixing:

Disk Utility does it’s usual routine, but it also does some checking and repair on the SSD portion of the Fusion Drive:

“Trimming unused blocks” is a function performed specifically on SSD drives. I am sure Disk Utility does other stuff on the SSD portion of the Fusion Drive as well.


Once I completed this function I Shutdown the iMac, removed the Tech HD and then booted into El Capitan. The bottomline is, startup of apps was a little faster, not a lot faster, but it was noticeable. If you wish to get a little more horsepower from the SSD portion of your Fusion Drive I would recommend this procedure.

However, I am not too convinced this slight increase of speed will help me extend the life of this machine. I am still considering upgrading my Fusion Drive SSD portion with a larger, faster third party one. Well, if you are going to all that trouble you may as well replace the regular HD with a new one because the spinning HD will die eventually right? I just have not made up my mind yet on all this. I have the experience and the tools to make the upgrade. It is a very difficult procedure because the 2012 iMac has the glued on screen. Getting into it and putting it all back together is a bear, but there are videos on how to do it.

I forgot to mention, to replace the SSD Fusion you have to “split out” the SSD from the regular HD. The only way I know how to do this is in the Terminal app. Then, when you are finished with the install, you can “recreate” the Fusion Drive using the Terminal, or just leave them as two separate drives. Complicated enough for you?

Oh, and one more thing. You need good backups to do this. When you “split out” the SSD Fusion it erases everything. So, when finished reinstalling you have to reinstall OS X on the SSD portion and then use Migration Assistant maybe, to move your apps on the SSD as well. Whew!! I am tired just thinking about it.


I will keep you posted on what I decide on this. I will be contacting various manufacturers of the SSD portion of the Fusion Drive (it is just a card really, like what is in a MacBook Air) to see what the speed improvement would be, if any. A very important factor is this. Replace Fusion SSD and the internal spinning HD about $500-600. Replace old iMac with new iMac about $2,000+.