The DS1522+ supports up to 10 extra bays and a 10GbE card
Two DX517 expansion units add 5 bays each over eSATA, and the PCIe Gen 3 x4 slot can take a 10GbE NIC or M.2 SSD cache adapter.
Two DX517 expansion units add 5 bays each over eSATA, and the PCIe Gen 3 x4 slot can take a 10GbE NIC or M.2 SSD cache adapter.