What’s So Great About Fusion Drive? (Part 2)

8/2/2013 5:54:05 PM

The dangers of D.I.Y

If you run into a software problem on your Mac while running a homemade Fusion Drive, support might be refused at a Genius Bar or a service provider until your Mac is restored to a regular configuration.

Use Time Machine for protection. With your backup drive attached start your Mac in the Recovery System by holding Command + R at the startup chime. In the option that restores from Time Machine, verify the most recent backup is listed. Backing up OS X this way gives a straightforward recovery if needed.

A Boot Camp partition can be preserved during the process, but back it up for safety. Windows Vista and later OSes have a backup feature, but require an external drive formatted for Windows. Alternatively, WinClone ($20, backs up Boot Camp from within OS X.



It’s possible to remove the Recovery System when setting up Fusion Drive, but that can be avoided by specifically targeting a partition. When creating a Mountain Lion install disk, take a USB flash drive you don’t need to reuse, so the OS X installer, Terminal, and Disk Utility are always to hand. Installing Mountain Lion to a drive from scratch will recreate a Recovery System on it.

Removing a Fusion Drive configuration requires starting from an install disk, opening Terminal. Use the command diskutil cs list and copy the code listed next to Logical Volume Group to the Clipboard. Type diskutil cs delete tap space, then paste the code and press Return. The internal hard drive is then independent of the SSD.

Fusion Drive Benchmarks

We measured these peak speeds from three storage options. Sequential data transfer is the best-case scenario. Random transfers involve accessing locations speed around a drive. Hard drives suffer most because of their moving parts.

Sequential read

Sequential read

Sequential write

Sequential write

Radom read

Radom read

Radom write

Radom write

6 steps to your own Fusion Drive

If you’re up for a bit of a challenge, here’s what to do…

1.    Back up your Mac

Open the Mac App Store. You’ll need to purchase and install Mountain Lion if you don’t already have it. Otherwise, click Purchases at the top of the window, locate Mountain Lion in the list and click its Download button. Once complete, the Applications folder will contain a file named “Install OS X Mountain Lion”.

Install OS X Mountain Lion

Install OS X Mountain Lion

If you already use Time Machine, open its System Preferences pane, click the Options button and check that you haven’t excluded system files, your user account, or any other folders from the top level of the hard drive from its backups. If you don’t already use Time Machine, connect a Mac-formatted drive, flick the switch in Time Machine’s preferences to On, and choose the drive.

Click the Time Machine icon in the menu bar, choose Back Up Now and wait until the backup is complete.

2.    Prepare a USB Flash Drive

You’ll need a USB flash drive with a capacity of at least 8GB, the contents of which can be erased. Connect it and open Disk Utility. Select the drive in the left pane – that’s the row that shows its capacity and model, not a partition already on eth drive then click the Partition tab.

Set the Partition Layout item to “1 Partition”. If the drive is bigger than 8GB, you can create more to use for other purposes, but there needs to be a partition that’s at lease 5GB on which to create an install disk. It doesn’t matter what you call this partition.

Click the Options button below the partition layout. From the three options presented, choose “GUID Partition Table”, and then click OK. Click the Apply button toward the bottom-right of the window and wait for the drive to be repartitioned and mounted.

3.    Create a mountain Lion install disk

Browse to the Applications folder and Control-click the Mountain Lion installer. Choose Show Package Contents, and then browse to Contents/ Shared Support and double-click InstallESD.dmg. Wait for the integrity of the disk image to be verified.

In Disk Utility, click the Restore tab. Drag “Mac OS X Install ESD” from the left pane into the Source box, and the partition on the USB flash drive into the Destination box.

Click the Restore button. You might be asked for your account credentials to proceed. It takes a while for the OS X installer to be copied to the flash drive.

In System Preferences, click Startup Disk at the far right of the row labeled System. Among the available startup disks you should see “Mac OS X Install ESD” with “OS X, 10.8.3” below it. Click it, and then click the Restart button.

4.    Look up essential details

When your Mac restarts, choose Disk Utility from the options. Eject then disconnect everything except the internal hard drive, the SSD, and the USB flash drive. Quit Disk Utility. Choose Utilities > Terminal. Type diskutil list and hit enter. Partitions are grouped by the disk to which they belong under rows starting /dev/ diskX (where X is a number). Two rows below those use the Size column to work out which is the SSD. To avoid wiping Boot Camp and the Recovery System, look for the partition with the name of your OS X volume on the hard drive. Note its identifier, such as diskXsY.

5.    Create a logical volume group

Type dikutil cs create Fusion then a space, then the identifier of your SSD, another space, then the identifier of your OS X volume. Press Return to create a logical volume group that identifies the storage that will be used by the Fusion Drive. Type diskutil cs list and press Return for a summary of what was created. In the row starting “+-- Logical Volume Group”, drag the pointer through the long alphanumeric code to select it. Press Command + C to copy it to the Clipboard. Make a note of the free space listed four lines below the code.

6.    Create a Fusion Drive volume

Type diskutil coreStorage create Volume then a space. Press Command + V paste the code. Type another space, then jhfs+ “Macintosh HD” and another space. Type the capacity noted previously. If it’s in gigabytes, use the form XXX.Xg, or X.Xt for terabytes. Press Return to create the volume. When done, look for a line that says “Finished Core Storage operation”. Quit Terminal, then open Disk Utility to see a device named Fusion and the volume just made on it. You can install a fresh copy of OS X or restore form Time Machine. The former is the best starting point. Migration Assistant can later transfer users, apps, and files from your Time Machine backup.

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