I have the new Mac Pro 6,1 w/~500GB internal PCIe-based flash storage. Currently ~150GB free. In retrospect, I probably should have gone with the ~1TB option. I keep most of my files on the NAS, but I'm sure I'll want more DAS sooner than later. Since I've got all these Thunderbolt ports, I'd just as soon use them, although the absolute fastest speed isn't really paramount. It so happens I have a couple of Seagate Backup Plus Desktop Thunderbolt Adapters, although I wouldn't necessarily HAVE to use them. Quick-and-easy solution might be a $429 480GB OWC Mercury EXTREME Pro 6G SSD (and stick it in a Seagate Backup Plus Desktop Thunderbolt Adapter). What else should I be looking at? ETA - while speed isn't paramount, the DAS should be at least 200MB/s read / write in order to merit being on by desk -vs- NAS (~100MB/s read / write). And ideally at least as silent as the new Mac Pro (which probably rules out the WD Velociraptor duo). ETA - I've tried a few "desktop" (2400 power-on hours) hard drives, but they require "Put hard disks to sleep when possible" in order to meet their duty-cycle and the spin-up delay associated with them annoys me.