Developer Patrick Stein a while ago posted Fusion drive on older Macs? YES! on his blog. A number of brave users are following his lead.
In the post he points out that Apple's Fusion Drive management software uses Core Storage Logical Volume Group, so we all can. To create the Fusion logical volume, users must enter a number of diskutil commands in Terminal.
After getting the homegrown Fusion Drive working, Stein, offered a few caveats and notes, including the news that he's using ZFS instead of HFS+:
Btw.: I will actually not use Fusion drive on a Mac as HFS+ is not really keeping my data safe (see my HFS+ fails miserably demo). Using two HFS+ disks concatenated just increases the risk of data failure. And TimeMachine as backup has failed me as well in the past.
I’m using ZFS to store my data ;-)
Addition 1: The SSD is a old Vertex2 so nothing Apple specific.
Addition 2: Mounting the drive with “-o noatime” does not change the caching behaviour, which is good.
Addition 3: I was using plain old 10.8.2, nothing special.
Addition 4: Before you see your drives in diskutil core storage you need to convert them with ‘diskutil cs convert’
Over at The Mac Performance Guide, the redoubtable Lloyd Chambers posted a detailed, multipage review of his experience building a Fusion Drive and posted some speed tests. It's an excellent piece.
When more stuff is stored than fits onto the SSD, the speed drops because the SSD has reached its capacity; Apple’s Fusion technology is not a caching solution.
At idle time, the Apple Fusion technology actively moves frequently accessed files to the SSD, and migrates infrequently accessed files back to the hard drive. Even portions of files (another consideration for recovery from a drive failure = a mess, be sure to have backups!).
There are some additional posts by Fusion Drive pioneers at Accelerate Your Mac. Reader Cedar says that he's "crossing his fingers ..."
I can't really say that I notice subjectively better performance, but it isn't worse either. Maybe it will take a while to figure out which files should be on the SSD.
I'm backing up frequently, (Time Machine and CrashPlan) but crossing my fingers that nothing goes wrong. (Not sure I'd trust a Fusion drive + FV at this point.)
I am attracted to this project since my primary machine is a MacBook Pro with a 240GB SSD and 750GB hard drive combo. Still, a homemade Fusion Drive really isn't for those who put a significant value on their data and potentially their time, if and when the setup comes apart. Maybe during an upcoming holiday weekend.
In the meantime, I'm testing out a cloud backup solution. Maybe that will give me more confidence in fooling around with this hack.