I personally don't like Drobo... I don't like parity RAID (especially for large media libraries where rebuild times become risky and downtime usually isn't critical) and Drobos proprietary solution even less. JBOD is perfectly fine for a media library. Did you look at the Oyen Digital Mobius I recommended? It supports SPAN arrays if your really want that, but those arrays have all the risks of RAID0 with none of the performance benefits.
Look at Raid Z2, no risk since you have a double redundant system if one drive fail rebuild it with confidence that the array is still capable to handle a 2nd drive failure while rebuilding the first downed drive.
RAID Z2 IS THE NEW STANDARD ON DATA CENTERS, builds on raid z2 require at least 4 drives, and become optimal for 7-8 drives, but is an big relief to the dual sucesive failure nightmare (it's likely you crash on a plane twice the same day)