I have the NAS server for a few days and am completely satisfied. Of course, I have not tested all functions. But so far everything worked immediately. In the meantime I have equipped him with a 3TB NAS HDDisk. The fan is far pleasantly quiet. Filling via the 1 gigabit or USB 3.0 port worked in the expected speed. Access via the Raspberry Pi or my Samsung SmartTV also simply and immediately folded. I was amazed (because not expect) that one (easy to change) or can connect USB hubs to the USB ports also Dockinstations for 2 hard drives. The so connected HDDs do not appear on the DLNA server, but are easy to operate via a PC. Through a web server is then added jobs to subdirectories on the server to move (or copy) without burdening the home network. Also terabytes of data can be as easy instalation.
Have now 2 3TB NAS hard drives in the server Zyxel. The additional HD was simply merged logically to the first. At times I have also connected 3 more HD to the USB ports, and so a file server with 14TB in my home network (via Samba). Supposedly you can include the external USB HD via the DLNA server (I have not tested).