Have a DIY Fusion Drive? Don’t forget ‘trimforce enable’ !

Posted on: 03:23 PM by Maurits

Since the introduction of the Fusion Drive by Apple I was impressed with the simplicity of use and overall performance of the Fusion Drive. It just feels like a large SSD.
In my Mac Mini 2009 I have replaced the optical drive with a third party SSD, and created a DIY (Do It Yourself) Fusion drive of this SSD with the existing hard drive. Read on how trimforce enable brings back speed to my Mac Mini.

My disapointment 🙁

So far the good part, the not-so-good part is the way Apple presents the Fusion Drive to the users. First of all there is Disk Utility, that only offers to ‘fix’ the Fusion Drive, which means ‘rebuild from scratch’, and now in 10.11 the User interface is even worse.
Secondly the limitation to support only ‘factory build’ Fusion Drive, while it can be the perfect upgrade for an older Mac.

Saved by the command line tools 🙂

Luckily there is the command diskutil coreStorage to make, repair and fix Fusion Drive, including unsupported configurations.

I know a lot of owners of older Mac’s upgrade their system by either replacing the hard drive with an SSD, or (specially when you have a large hard drive) replace the optical drive with and SSD (with a special kit, available on places like iFixit), and create a Fusion Drive from the internal hard drive and new SSD.
Procedures are available on the web and here , but the basic commands you need after placing both disks look like this:

diskutil cs create ‘Fusion Drive’ /dev/disk0 /dev/disk1
diskutil cs createVolume 12345678-1234-1234- jhfs+ ‘Fusion Drive’ 100%

I did it on my own Mac Mini (2009) that I use as an experimental server.
Two tips if you have plans to do this:
– have (and keep) an good backup; Fusion Drives are complex and due to two storage devices at least twice the chance to break.
– check the type and speed of the connector for the optical drive. On some machines (MacBook Pro 2008) this is ATA , not SATA!, or in the case of the MacBook Pro early 2011, the optical connection is 3 Gbps SATA, while the other is 6 Gbps. Place the SSD on the fastest connection.

Since 10.10.4: trimforce command

On my demo server (that I use rarely, and even then mostly with Apple Remote Desktop) I noticed that it felt much slower than it used to be. First I blamed the newer OS versions, but than I realised that my unsupported SSD will not enable TRIM by default.
And Fusion drive will do a lot of writing and deleting to SSD (after moving to hard disk), so TRIM support can be essential.
Since 10.10.4 Apple has included TRIM support for unsupported SSD’s with the command
sudo trimforce enable
You will get a huge warning in ALLCAPS that it is not supported, but it works with most SSD’s.
Check in System Information; it will show wheither TRIM is enabled or not.
Note: You need to redo this step after re-installing the OS, and check after upgrade the OS.


Now my demo MacMini 2009 feels much faster with my DIY unsupported Fusion Drive.

If you have a similar setup, please check if you can enable trim this way (after double checking your backup 🙂 )

Related training courses from LAI

Learn about TRIM in our ACMT training. Learn using the command line in our training OS X Command Line.

Questions? See my info on the contact page.


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