I just ordered a Retina iMac and after much anguish decided to go for the base 256G SSD (was considering a Fusion drive or 512G SSD as options). Part of my reasoning is that I'd prefer to avoid a spinning disk inside my case (suspect it is part most likely to fail, and would prefer to minimize risk of having to open up case or send it in to be serviced). My Windows 7 box is currently running on a 256GB SSD, and while it's a little tight I'm getting by (have a NAS for backups and media storage). I'm hoping that in a year or two, I can add fast external storage for less than the $330 to upgrade to a 512GB SSD. An option that looks appealing to me is making my own homebrew Fusion drive by sticking a 256G SSD and (say) a 2TB HD in an external 2-drive TB enclosure (such as http://eshop.macsales.com/item/OWC/METB7DK0GB/). As a sanity check is there anything I'm overlooking that would make this painful or infeasible? No problems enabling TRIM on an SSD in this fashion? Quiet is somewhat of a priority for me - would the spinning HD be put to sleep/parked most of the time (assuming most data is being served from the SSD part of the Fusion drive)? Any thoughts on type of HD to buy for this application (ie WD Green? Black? Blue?). Currently, this would be a bit pricier, at something like $250 (enclosure) + $120 (SSD) + $95 (2TB WD Green?), but I suspect those prices will fall a bit before I'd actually need it, and it would result in a 2TB Fusion drive with a beefier 256G SSD (plus the 256GB original iMac drive) instead of just a 512GB internal for $330 more. Any advice on issues above, or thoughts from those who have rolled their own Fusion drives, would be appreciated.