Drobo calls it “beyond raid”. They would say it’s neither. A quick view of their front page video would be worth the look.
The 256 mSATA card acts basically as a cache and can improve read speeds up to 3x’s (they claim).
I’ve used them for years, and the beauty of it is it maintains itself, you can throw any drive in there (any make, model, size, or speed) and the update the firmware as drives get bigger. You also don’t have to completely fill up all the bays so it’s very expandable. And it let’s you know when a drive is going out or has failed and has built in protection. Hence the name drobo, it’s supposed to be a data robot and do all the work for you.
They aren’t necessarily fast enough, if you got the 5Dt w/Thunderbolt 2 it would probably be fine. I’m using the old Drobo S via USB 3.0 and cutting 4k stuff, and it’s actually not been bad. No mSATA on my chassis.
They do have problems mounting sometimes, which is why I was looking on here. Occasionally lots of rebooting is necessary, but it has always shown up eventually.
So I’m a fan for the price-point and expandability!