The Asustor AS5404T's NVMe slots work as actual storage — not just cache

Most NAS makers treat M.2 slots as a speed bump — cache-only, no permanent storage allowed. The Asustor AS5404T is more generous: those two NVMe slots can host a full storage pool alongside the four SATA bays, so you could run an all-flash pool or tier your data without sacrificing a drive bay.