A few weeks ago, I took out my early 2011 13-inch MBP's optical drive, put my 500GB HDD in the optical drive area, put a 120GB SSD where the HDD used to live, and made a DIY Fusion Drive according to the instructions at Macworld's website. I got amazing results at the time (a formerly-1:21 boot time became 0:18!), but a few weeks later, I tend to get rather un-Fusion Drive-like speeds. I've seen Fusion Drives duplicate a 4GB file in 21 seconds (source), but a test run I did just now took 1:31. What can I do to restore my Fusion Drive to its youthful glory once again?

2 Answers 2


What make SSD?

Samsungs may need a firmware update & performance restoration to prevent slowdown [scary, done in DOS, using very inadequate instructions from Samsung, I've not yet braved it]...

...or you could try TRIM Enabler which may go part way towards speeding it up again.

  • It's Samsung, but I'm not sure how to make the firmware update happen on OSX. There's also the fact that it's been totally reformatted to be part of a Fusion Drive, if that means anything about its firmware. I'll try TRIM Enabler, since I know Yosemite didn't exactly play nice with TRIM. Thank you!
    – user24601
    Nov 28, 2014 at 8:16
  • The firmware runs below the format level - but idk about how it would affect the 'fusion' aspect. My guess is that it would have no effect, as it's below the format; but updating a drive's firmware is not something you should attempt without a full backup anyway.
    – Tetsujin
    Nov 28, 2014 at 8:19
  • 'The Hard Way' does exactly the same thing as Trim Enabler will do for you, except, by the look of it, bypassing the kext protection. If you do that on Yosemite, you'll very effectively lock yourself out of your machine. Prior OSes don't have kext signing, so it doesn't make any difference which way you do it, except TE is one button ;-)
    – Tetsujin
    Nov 28, 2014 at 8:33
  • 1
    Funny story... apparently I'd already disabled kext signing earlier, by upgrading my AirPort card and modifying the necessary kext to support Handoff. No more apprehension about Trim Enabler!
    – user24601
    Nov 28, 2014 at 8:35
  • I just ran the 4GB test post-TE reboot, and no change...
    – user24601
    Nov 28, 2014 at 8:47

There is no need/possibilty to fix that. This is a common behavior of Fusion Drives.

The Fusion Drive ("CoreStorage" in the pictures below) usually contains a logical volume group, a combination of a SSD and a HDD).

After installing your system and some applications you'll get full SSD-speed copying a test file because all the files reside on the SSD:


Installing more applications and having more "high priority data" the SSD will be full and the only possibility to copy data to is the HDD. The test file will be copied with HDD-write speed:


Over time your TestFile and some other low-priority data will be slowly swapped to the HDD, because you'll have even more high-priority data. The TestFile loses its high-priority status because of low accesses. The TestFile will be copied with even less than HDD-write speed because it has to read/write from/to the HDD at the same time:


Even if the TestFile regains a high-priority status because of frequent accesses a resulting copy will be copied to the HDD with accordingly low HDD-write speed:


Please check this answer to determine where the TestFile may reside and where the TestFileCopy is written to.

Some more usefull information: arstechnica and wikipedia.

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