What is Fusion Drive?
Fusion Drive is Apple new fusion (geddit) of a traditional spinning hard drive and a modern Solid State Drive (Witchcraft. Burn the witch!) It stores the bulk of your data on the slow but spacious spinning drive while moving often used data (applications etc) to the faster SSD. (Burn the witch!)
Why is a Fusion Drive?
Until now computer hard drives have been divided into two basic types. Traditional drives consist of many spinning platters with a read write head that flashes back and forth hunting down data stored on the magnetic surface of the drive platters. Spinning drives. The new kids on the block are Solid State Drives (SSD's). Made from the same stuff as the RAm on your Mac, these drives offer access times to your data that are orders of magnitude faster than any spinning disk could manage. Which is nice. Spinning drives offer large amounts of storage for a relatively small price, a 1TB laptop drive weighs in at around £75 while a 3TB desktop drive may set you back £150. Contrast this with an SSD which is blazing fast but a mere 128GB of storage will set you back £80 while a 756GB drive will cost upwards of £800. Which is a lot. The fusion drive is Apples answer to the perfectly reasonable desire to have the best of both worlds.
How is a Fusion Drive?
Luckily, quite easily. Apple currently only offer Fusion Drive on the top end models of the new iMacs, but it's perfectly possible to add this technology to an older MacBook Pro or even an iMac.
You will need a few things in order to create your own Fusion Drive, or as I'm going to call it to save typing FD.
An SSD (128GB or more for best effect)
A new spinning drive (you can reuse your old one if you want)
An optical drive bay caddy to house the second drive
A solid backup of all your data. Later on we will be breaking out the Terminal, which offers endless opportunity to loose all your data. YOU HAVE BEEN WARNED!
Remove your old hard drive and optical drive. The second drive in the FD setup lives in the vacated optical bay of your laptop (or iMac). You won't be able to burn or watch DVD's any more, but hey! Steve hated DVD's anyway. Steve would have been happy. The best place for the SSD is in the original hard drive bay. If you have an iMac you'll need a mounting kit as SSD's are a smaller form factor than the drives in iMacs. Put the spinning drive in the optical drive caddy and replace the caddy into the vacated optical drive space. Here's one I did earlier…
Once the Mac is back together the fun begins. You will need to boot your Mac from either and external hard drive or the recovery partition of your original drive. Fusion Drive requires OSX 10.8.2 or later.
Once the Mac is up and running you'll probably get an error message saying that your SSD or new HDD need initialising. You can ignore this. If you are booting from the recovery partition, you won't see hte message anyway.
Fire up terminal. Disk Utility can't create fusion drives yet.
In terminal type diskutil list
This will list out all the partitions on your drives. You'll need to identify the partions that represent the SSD and the spinning drive. This should be obvious by the sizes and names of the drives. Normally the drives will be called disk0 or disk1 etc
Fusion Drive uses CoreStorage to create what is called a LogicalVolumeGroup to do this type diskutil coreStorage create "your hard drive name" drive 1 drive 2. So, if I'm going to be using disk0 and disk1 I'll type diskutil coreStorage create myLogicalVolGroup /dev/disk0 /dev/disk1
Wait for terminal to finish creating your new logical volume group. Once this happens Terminal will assign a unique identifyer for your new drive. You'll need to cut and paste this.
type diskutil coreStorage createVolume "UUID here" jhfs+ volumename 100%
to break this down, UUID is the UUID from the last step, jhfs+ tells the Mac to crete the volume as an HFS+ volumename is what you want to call the drive and 100% tells the Mac to use all the drive space.. I called my Fusion drive, well, Fusion Drive. If you have a space in the volume name you must add quotes at the start and finish, so you get diskutil coreStorage createVolume "UUIDhere" jhfs+ "Fusion Drive" 100%
Bingo. You now have a fusion drive. Close terminal and use the recovery partition to reinstall OSX and then migrate your data over.
Things I found out.
While the whole process was pretty painless I did discover a few things that are worth mentioning.
You need to make sure that your spinning drive is in good shape. My first drive seemed fine, and booted the Mac OK. In fact it's still running fine, however there were hidden errors in the partition map which caused diskutil to choke so I had to get a second drive ready.
Take care in diskutil as the form of commands is vital. creating your Fusion Drive wipes all your data out so BE BACKED UP!
Installing OSX and migrating was a snap. However there was initial disappointment. Boot time seemed only marginally faster and the machine felt sluggish still. Worse, the Mac would not wake from sleep. Oh dear, what had I done.
Luckily patience was my friend. Because of how fusion drive works there was obviously a fair amount of behind the scenes disk activity taking place in addition to spotlight indexing the drive. Once spotlight was done and an hour or so had passed, performance began to pick up.
Fusion Drive also seems to need to learn what data to move to the SSD so initial launches of applications can seem to lag, but after than they spring to life like Olympic sprinters.
One day later, boot time is now a fraction of what it was and broadly in line with a vanilla SSd install. A 750GB SSD would have set me back over £500. My home brew Fusion Drive cost me £80 for the SSD, £25 for the caddy and about an hour of time.
Please note: A lot of what is outlined here can permanently remove all your data. Anything you do here is entirely at your own risk.