My box comes complete with four 10TB Seagate Exos drives, two 512GB SSDs (cache only) and 16GB RAM (that's more than from the CPU manufacturer specified and 8GB specified) supplied by Asustor). max but recognizes 16GB and I haven't had any problems yet). The hardware is top notch and comes from the folks at Asus. The only limitation I have is that I come from a Synology machine that is 4 years old and the software is definitely more user friendly than Asustor. If you like working more with software and are up to the task then by all means buy Asustor, but if user-friendly software is your top priority you might be better off with Synology as their system DSM is a bit more user-friendly. You really can't go wrong with any system, but I find the hardware performance of the AS6604 better than the similarly equipped Synology 1520.
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