I installed a 240GB mSATA SSD, as a cache drive in my Drobo 5D.. First thing, I was really shocked to see how small this thing was. Second, I didn't realize it will have that much impact on the performance, mainly write speed. Data is copied to SSD, then moved to the slower HDD drives.. A 20MB file didn't even show the copy thermometer.. Drag, drop, and it's there.
I'm mainly using the Drobo as my main storage for my digital assets.. I have digital photographs dating to the year 2000, and some family videos. All were previously stored on several external HDs, and data CDs/DVDs. I panicked when one of the HDs had a hiccup, which was luckily repaired. But I didn't think I'd be that lucky again.. So, the Drobo 5D was my choice for a home RAID system, with five 4TB drives; three for storage & two for parity protection.