The ASUSTOR Xpanstor 4 (AS5004U) is a 4-bay expansion unit that adds storage to an existing ASUSTOR NAS over a 10Gbps USB 3.2 Gen 2 Type-C connection. It is backward compatible with ASUSTOR NAS models that only offer USB 3.2 Gen 1, running at 5Gbps there. The four hot-swappable SATA bays accept 3.5-inch or 2.5-inch drives, for up to 88TB of raw capacity with 22TB drives. It powers down when the connected NAS sleeps or shuts down, and a 120mm smart fan adjusts its speed to drive temperature. The included USB-C cable screws into the unit so it cannot be knocked loose, and it also supports ASUSTOR's MyArchive cold-storage drives. Plug it straight into a Windows, Mac or Linux PC and it works as DAS too. In the box: the AS5004U, a USB 3.2 Gen 2 Type-C cable, a 90W adapter and cable, 2.5-inch drive screws and a quick installation guide. Drives sold separately.