The WD 4TB My Book Thunderbolt Duo is a dual-drive storage system with two Thunderbolt ports capable of up to 10 Gb/s data transfer rates. The system supports user-selectable RAID 0 and RAID 1 modes, as well as JBOD modes. Plus, since Thunderbolt ports are bidirectional, they afford high-speed multitasking. You can also daisy chain multiple devices or peripherals using the two Thunderbolt ports for better efficiency and productivity. For added convenience, the drives are user-serviceable and the system comes with the WD Drives Utilities software.