Western Digital has already dialed things up to 4TB with its My Book Studio Edition II hard drive, and it’s now done the same with its new My Book World Edition II dual-drive storage system. One of the large advantages with this one is that the dual drives are shipped in a mirrored RAID 1 configuration for an extra level of protection, even though you can of course reconfigure ‘em yourself if you’d prefer twice the space instead. Otherwise, you can anticipate all the usual NAS-related features, a “cooler, quieter, eco-friendly design,” a USB port to add on an extra USB drive, and a nifty capacity gauge to let you see how much space is available at a glance. Expectedly, the top-end 4TB demands a rather hefty $700, but you can also pick up a 2TB drive for a more reasonable $400 if you have less demanding needs.