I finally got my 2012 27" iMac without a fusion drive because I couldn't wait for a bto. I will not stay without one though! I intend to buy the Seagate GoFlex Thunderbolt adapter and either a Samsung 830/840/840pro or an OCZ Vertex 4 SSD 256GB drive. My question to those who have fused the internal 1TB with an external SSD: If I partition my SSD to 2x128 GB partitions can I use the first 128 GB as part of the fusion drive (in combination with the internal 1TB) and keep the second one as a spare drive for my files ? A bit tricky huh? And in general are you satisfied by the performance of your external fusion drive? What speeds do you get and do you have any issues? And a silly question: what if the external drive accidentally gets disconnected ?