Yes! You may attach as many external hard drives or USB drives to your Pogoplug Device as it has open ports to accommodate them. Our various models have differing capabilities, so see our hardware comparison chart in order to better understand what is compatible with your device. The latest model, the Series 4, for example, comes with two USB 3.0 ports, one USB 2.0 port, an SD card slot, a 2.5-inch SATA connector, and an Ethernet port. In addition to these ports that come out of the box, you may attach a USB expander into the device to add even more hard drives.