Drobo Minifrankspin June 21, 2012
Drobo offers four hot-swappable drive bays support drives of any capacity.The Drobo Mini is a 4-bay storage array supporting 2.5" SATA drives for on-the-go redundancy for up to 3TB of storage.
It's got USB 3.0 and Thunderbolt ports, which means you know it should have some pretty high read/write speeds. If you're someone who is mobile a lot and worried about your data, this seems like it's a good fit.

At 2.2lbs, minus drives, it's not the lightest thing but it's still pretty portable, and far lighter than some of the other Thunderbolt-based RAID arrays out there. One big reservation with this is that while redundancy is great, making something portable means it becomes more susceptible to drops which we all knows means something can break.
http://gdgt.com/discuss/drobo-releases-the-first-portable-storage-array-providing-on-the-go-redundancy-but-would-you-benefit-from-it-1a8r/http://www.drobo.com/products/professionals/drobo-mini/index.php