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I've succesfully built a fusiondrive on my late 2009 iMac (256Gb Samung830+2TB HDD). I set the size to 100%, so I have no recovery partion. However when I boot with the option key I get two identical volumes to chose from. Clicking one or the other brings me to the desktop. I've seen this reported elsewhere, but is it normal on a DIY fusion drive? My iMac runs fine and snappier and the drive shows up as one in Disk utility. Could indicate that some kind of special firmware on the SSD is needed to get a "fully" functional fusion drive?

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Fusion Drive utilizes a component of OS X called CoreStorage to work. When you boot your Mac holding down Option, you are booting into a screen running in the low-level EFI environment, before OS X has started. EFI doesn't understand what a home-built Fusion Drive is, but sees two physical drives capable of booting into OS X.

I'm not sure of the mechanics of why factory-built Fusion Drives in the latest Macs act differently but my guess is that there is a firmware chip of some sort, like you said. Apple is known to put custom firmware on some of their hard drives.

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