I purchased a 'Refurbished 27-inch iMac 3.4GHz quad-core Intel Core i7' from the Apple UK refurb store in March 2013 with a 3TB Fusion Drive. It has been fine up until I installed Yosemite when it started to freeze all the time and I had the spinning ball all the time. Only way to get back was to hold the button at the back and reboot. Kept doing this until I backed up and did a clean install of Yosemite. Fine for a week or two then happened again. I have just wasted a whole day trying to go back to Mavericks and it worked fine for an hour or two then went the same way, spinning ball, unresponsive so I can eliminate Yosemite now as it is fine on my Macbook and has been since the day I installed it (same day I installed in iMac). Just tried another clean install but it first said the HD had failed and do I want to repair the Fusion drive? My guess is that the SSD is fine but the other drive is dying a slow death. Have a genius appointment booked in for tomorrow so will take it up there to see what they say. Any idea on what price I am looking at for a Apple to fit a replacement 3TB HD at all? Paid £2k for this and not done 2 years yet so not best please and dubious about going for another Fusion Drive again. Didn't take Apple Care although should have really, especially with a refurb. Hindsight eh! Just tried again to re-install Mavericks and getting 'Install Failed' The Installer could not start the computer from "Macinotosh HD". Try selecting your disk using the Startup Disk utility. Sad times.