Let the hive mind of Engadget get that for you.
"I finally got a new laptop with a lone USB 3.0 port. I'm now looking at getting a USB 3.0 hub with a power adapter so I can use both of my USB 3.0 hard drives at faster speeds. I've read lots of horror stories where some hubs either don't come with power adapters -- and as a consequence the portable drives don't work with them properly -- or they are designed poorly which results in USB 2.0 speeds. Or, the hard drives keep getting disconnected. Do your readers have any suggestions or experience using USB 3.0 hubs? Thanks!"
This would only have 3TB usable space in a RAID0...RAID5 would be 2.25TB, and RAID10 (if this thing is even capable of nested RAID) would be 1.5TB. I don't know of anybody who would need 3 terabytes of space who wouldn't want at least some form of parity for that amount of data.