In October 2012, Apple announced Fusion Drive as a feature for their consumer desktop Macs. Within a week, Ars Technica’s Lee Hutchinson wrote an article about the viability of building a Fusion Drive for any Mac running 10.8.2 based on some initial research by Jollyjinx. Two weeks later, Macworld did some real-world testing and provided some easy to follow instructions.
Coincidentally, my girlfriend’s Late 2009 iMac’s 1TB spinning disk was getting frightfully full. Knowing that we hadn’t used the optical drive in ages, I decided it would be a great opportunity to go Fusion (and the holidays were right around the corner). I snagged a 3TB Seagate drive and went to OWC to grab a 120GB Mercury Electra SSD. I knew I was putting this in an iMac’s optical drive slot, so I knew I’d need an adapter. Luckily, I found one at iFixit.
The hardware installation went great, especially when we ended up having the iMac drive temperature sensor in stock to replace the firmware-fed sensor that the machine came with. Once I got it back together, I went ahead with the software install. I created a 10.8.2 install disk from my InstallESD.dmg file from my Install OS X Mountain Lion.app, booted from it, formatted each drive using Disk Utility, and went ahead with the diskutil Terminal commands. After the logical volume was created, I went ahead and installed OS X.
Installing iStat Menus allowed me to keep track of disk I/O as I installed software, configured the machine, and transferred data. In short, the algorithms Apple has in place heavily favor the SSD, but as soon as your drive reaches a certain allocation, the HDD bias affects access to large libraries of data. Overall, I was pleasantly surprised with the speed of booting and launching apps and greatly appreciate the ease of not having to manage multiple volumes. It’s been a month and I can happily recommend this solution to anyone eager.
Just remember — don’t forget to back up. (I’ve got Crashplan, SuperDuper, and Time Machine all working simultaneously.) If you want a bit more of an in-depth analysis of the pros and cons of Fusion Drives, I highly recommend Anand Shimpi’s article.