This is my first iMac. I bought a 27" 3 TB fusion. Originally I had planned to take my new iMac to Apple and have them transfer the data. That wasn't to be, I caught pneumonia and in my extremely frigid climate (-25C to -35C) it might be March before I'm well enough to leave my house (I have other health issues that make life more interesting as well). So the plan was to do the migration myself. The first attempt was through wifi and thankfully it crashed as it was going to be days before it would complete. I then moved to using Ethernet. It took 3 tries with Ethernet before the migration finally took. It also meant I had a few calls to Apple to figure out what was going on. Since I was new to iMacs I didn't totally understand what was going on and interestingly enough it seems some of the support folks didn't either. Because I had 3 failed data migrations I had loads of data on the HD that the iMac could tell me it had but couldn't access. My first Senior Advisor tried to tell me that this wasn't a problem and just to do another migration. Luckily this one failed too and the next Senior Advisor I spoke was much better. Basically he said since the transfer had failed, the process hadn't completed and the iMac didn't know what to do with imported data. His recommendation was to scrub the drive and start again. We deleted the contents on the HD and reinstalled Mountain Lion. From there I started my 4th attempt to migrate my data. Thankfully it worked and I'm now working on my new iMac. What was clearly evident in speaking with both Senior Advisors is that at this point, they really do not fully understand the fusion drive and how it functions. The first Advisor was seemed to think he knew what he was doing (and did not take the time to read through any Apple provided materials) the second Advisor explained that the newness of the fusion drive meant he wasn't well versed with the fusion drive but he was very happy to spend the time to make sure we did the right thing. I'm very happy to have it all working now, but it was a little unnerving to get to different solutions to the same problem.