Buffalo TeraStation Duo dual drive NAS device with RAID capability. With RAID 1 and Hot Swap functionality, if a drive does fail, the TeraStation Duo automatically powers down the faulty drive, enabling you to safely remove and replace without losing any data, or down time. The replication function allows the connection of a second TeraStation Duo via the USB or LAN port and replicates the data to improve reliability, fault tolerance or accessibility.