I upgraded my 2011 iMac with a DIY Fusion Drive about a year ago. Samsung EVO 840 250GB SSD and a Seagate 3TB HDD, works great! Not as fast as pure SSD, but much better than pure HDD and I have over 3TB capacity. Best compromise for me. When I look at the drive operating temp, I am guessing that's the temp of the SSD, not the HDD??? Can anybody verify this? I think because my SSD is mounted under the Optical drive without any fans or good airflow that is causing it to run a bit hotter, which in turn makes my drive fan operate more faster and more loudly than I'd prefer. Considering putting a little fan in the case which points at the SSD to help keep the drive temp lower and the system drive fan spinning lower and quieter. Thanks!