On-the-fly SAS expansion up to 12 additional bays RXD1219sas is a 2U expansion unit designed to work automatically when connected providing an effortless storage space upgrade solution for your Synology servers 1. You can add up to 12 additional 2.5 / 3.5 SAS drive bays on the fly when connected directly with a mini-SAS HD cable. Designed for maximum reliability The redundant power supplies ensure maximum service uptime. On the rare occasion when a failure occurs you can instantly replace the hot-swappable drive trays & with the key system components modularized SAS modules & system fans can also be replaced with ease. High-performance data transmission The mini-SAS HD provides high bandwidth connectivity to achieve maximum throughput during data transfer between your Synology server & RXD1219sas. It allows the drives in the connected RXD1219sas to operate as if they are the internal drives of the Synology server with no data latency..