DIY Fusion Drive

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by

Mike Moffit
in

Some of you may be aware of the so called “Fusion Drive” technology available as an option in the newest line of iMacs (released late last year). This software technology allows for two different physical internal drives to be acknowledged as one by the system. The idea is to have one of the drives be a solid state drive and one a traditional hard disk drive. As you go about your digital business, the system learns what data is accessed most frequently and allocates it onto the SSD for the fastest read/write speeds. Subsequently, it puts less-accessed archival data onto the HDD where speed is not required.

For those speed hounds and DIY lovers out there, this pseudo-RAID technology can be brought to devices other than the new iMacs. According to an article by Tom Nelson found here your machine just needs to be able to run OS X Mountain Lion (10.8.2 or later). If your machine is up to snuff and you feel comfortable undertaking the task, then here is a tried and tested method of making your own Fusion Drive:

Prep for Fusion

  • BACK UP YOUR DATA! Goodness, this can never be emphasized enough, but in this case I can say unequivocally that the data will be erased on both your HDD and SSD in order to complete the fusion. Best bet is to use an external hard drive and make a Time Machine backup.
  • Create a bootable copy of the 10.8.2 or later installer on an 8GB thumb drive.
  • Install both the HDD and SSD in your machine.
  • Boot to your installer thumb drive by holding down the option key during startup.
  • Open Terminal (in the utilities tab in the menu bar).

Terminal Commands
In Terminal you will enter the following commands. Please write these exactly as they appear. The exception being, any words in quotations will be replaced with information you discover as we go. This will become clearer as you go.

  • diskutil list
  • Press Return
    you should see a list of available drives — take note of the disk identifier correlating to each drive; you’ll be able to tell by the size.
  • diskutil cs create "drivename" "driveID1" "driveID2"
    The drive ID is the number from the previous note and the name is whatever you want it to be.
    To make sure we’re on the same page, an example of what this command should look like is: diskutil cs create Fusion disk0 disk1
  • Press Return
  • Wait while the command is running. When it’s done, continue.
  • diskutil cs list
  • Press Return
    Copy the Logical Volume Group ID, which is a string of alphanumeric characters separated into groups by hyphens. Then note the free space available, which will be transcribed in GB even though it appears in TB i.e. if there are 1.1TB available, you will write in the next step 1100g
  • diskutil cs createVolume "groupString" jhfs+ "volumeName" "size"
    The groupString from before is what you copied, the volumeName is what you want to appear beneath the icon on the desktop (typically Apple names this Macintosh HD). For example the command could look like diskutil cs createVolume 352D9D2B-E0F2-4A16-B583-A257802EC74C jhfs+ "OWC Fusion" 1100g and yes, there are quotation marks in that command because whenever you want a space involved you use quotations
  • Press Return
  • Quit Terminal

Wrapping It Up

  • Now you’re back at the main install screen, so select the icon for the Fusion drive you just made and proceed with installation. An internet connection is required for this process to complete, as downloadable updates need to be installed.
  • Use Migration Assistant to restore your Time Machine backup and BAM, you’re done.

This process may look tedious and difficult if you’re not comfortable with Terminal, but I assure you it is straight forward if you’ve read everything carefully. Please be in touch if you try this and your computer explodes, that would be a first for me! But please don’t tell me I didn’t warn you to back up your data first.