I currently have a Lacie thunderbolt external drive that is 3tb hard disk. I use it as my overflow to keep files that really don't need the speed of my 500gb SSD inside my iMac. The drive is great but I have found that I have filled it up rather faster than I had anticipated and have come to the other side conclusion with my iMac with the OS. Apple does like to bring out a new OS every year and sadly to say the upgrade process for me has not been that smooth. It would be nice to have the option to try it out for a bit on an external drive to make sure it works fine before committing to the internal. I have tried several USB3 solutions that turned out to be more trouble than help. I am wondering if going big like a OWC Thunderbay 4 or the mini would be a worthwhile investment. I have only had this iMac for 1.5 years and can't see myself affording to buy another in the next few years (or six). I gather that thunderbolt is a stable connection and offers some advantages over USB3. I don't know how long the Lacie will last for, it is a spinning hard drive so it has the average life expectanty warranty of a couple of years but unlikely to make it to 7. Is going an open standard drive bay that you can add/remove/change drives as need a better investment over buying just another USB drive for $140 and knowing it's just a 1-2 year solution until it dies and then get another? What do others do with the yearly bug patch/upgrade for their iMac?