[RndTbl] NAS box

[Adam Thompson]

LJ has ads from Polywell every month, I'm pretty sure they have something up your alley.  (www.polywell.com/us/lx)
You could also use the BeagleBoard, buy a 2-disk SATA hotswap tray, and a chassis, but you can't use a standard distro.
You could always rig up to eSATA enclosures to pretty much anything that supports eSATA... Or USB, albeit at lower performance.
The two-hotswap-bay requirement will likely have you either using external equipment, or an ordinary ATX mid-tower case... Regular 5.25" bays also get you reasonably cheap hotswap trays.
Size-wise, almost no-one bothers making OEM product at the 2-disk level; there's tons of options in 19" units or 8-bay towers.
How much are you willing to spend?
-Adam