Here's the heartbeat of the set up -- my drive enclosure - it's a Media Sonic with two 2TB WD Red's. They aren't set up as raids - just drives which are mirrors of each other. I'm a photographer - and this is where my photos reside. Speed isn't a concern as this is just a repository - the LRoom library is on the main MacMini drive.
Whenever I import photos to LRoom from my memory cards - it's a dual push to both drives. I'm also subscribing to BackBlaze - which pings a backup to the cloud. Backblaze is a bit different than Carbonite -- where Carbonite doesn't pull from tethered drives with the base subscription, where BackBlaze does. A very key distinction.
Drive bay was $100 and drives run about $125 - RED's because they are robust enough for NAS enclosures and from what I've read - the WD Greens don't respond the same in enclosures.
Why not Drobo -- well - the expense is one - and the proprietary FAT has me wondering. I'm still researching the system - I can see myself going to it eventually - just not now. They've made some gains with the new system from what I'm reading in Scott Bourne's recent review.
I'm pretty happy with the Media Sonic - it's really quiet - and I've rid the studio of individually powered USB drives - where now they are all wrapped in one device.