The Asustor AS6604T follows the same caching-only NVMe approach

Like its 2-bay sibling, the 4-bay AS6604T gives you two M.2 slots that only handle cache duty. The four main SATA bays take both 3.5-inch HDDs and 2.5-inch SSDs. If you want NVMe for actual storage, step up to the AS5404T.