The RX1217RP is a 12-bay storage expansion unit that adds capacity to a Synology RackStation — it has no compute of its own and works only when connected to a host NAS. Its 12 hot-swappable bays each take a 3.5" SATA hard drive, 2.5" SATA hard drive or 2.5" SATA SSD. The unit connects to the host RackStation via an included Infiniband cable for maximum data throughput, and three 80mm fans cool the drives and the unit itself. The RP model carries two redundant 500W power supplies, so it keeps running on the second PSU if the first fails — the one feature that sets it apart from the standard RX1217, which uses a single 500W supply. It's built specifically for Synology's RackStation range.