While awaiting the new 27" iMac, I bought a MacBook Air with 128 GB SSD and 6 TB Thunderbolt storage (3 TB RAID1) for my data, which is nearly full. I wanted to use the same setup for the new iMac, only then with a 512 GB SSD (as 128 GB is not enough on the long term). But then the iMacs came out and it became clear there were no realistic SSD options. No 128 GB, no 256, no 512... only a 768 GB SSD (whose idea is this!?). As this is more than I need and far too expensive (€ 1300 which equals $ 1800 extra) I'm looking into other options. 1) Opening it up when it arrives, replacing the HDD with an 512 GB SSD 2) Using a 512 GB SSD (Thunderbolt) as external boot device (with OS X on it) 3) Forget the true-SSD thing and buy a Fusion drive 4) Don't buy and wait for the Mac Pro 2013 All options aren't exactly ideal. Option 1 will void warranty. I don't know how easy it is to replace the HDD with an SSD. It looks pretty accessible, but didn't Apple use proprietary connectors in the past? And how do I close the machine again using foam tape so that it still looks as new...? Option 3 is something that doesn't fulfill my needs, but if nothing's possible, this is the only option I see myself ordering a Mac. I'm using SSD's for years now (for the OS), so I think it's a step back. Option 2 is probably the most interesting because I don't need to open the case and I can choose the standard 1 TB hdd, so I save some money. The thing is... how risky is it to use ONLY external storage? OS X will be on the Thunderbolt SSD, so not inside the machine. And the majority of my data will also be on another external Thunderbolt drive (with two 3 TB hdd's). How will OS X and all programs handle this? Could there be issues when upgrading to a new version of the OS? I guess 99,99% of all Macs use internal storage, so I can imagine the OS would have trouble with exceptions such as my setup...? Can you think of any issues? Or is this the most logical option for me?