I have a DXP4800+ with Truenas installed, but for the life of me I can’t seem to be able to see my external harddrive (with existing data) in my network when attached. I only seem to be able to add it to anything if I first choose stripe and wipe it
That’s exactly what TrueNAS does–its own storage. Put drives into the four bays on your device, create a pool on them, and share away. If all you wanted to do was put random USB drives on the network, you wasted quite a lot of money on that NAS.
The four bays will be fully used, but copying files from external drives directly to the bays is faster. Synology and Ugreen OS can do this. Plus I can also see them on my network, which is nice from time to time.
I reverted to UgreenOS, so only time wasted. Truenas was not my usecase, but glad I tried it.