I have always kept it simple. A storage array in JBOD (non-raid) setup. I buy two of whatever drive(s) will contain the duplicated data and just do a clean mi

I have always kept it simple. A storage array in JBOD (non-raid) setup. I buy two of whatever drive(s) will contain the duplicated data and just do a clean mirror using whatever backup software you desire. I happen to use 4TB HGST drives in a Mediasonic PROBOX 4 tower hooked into a PCIe card in my computer that connects them all through one multichannel eSATA cable. The software I use is Allway Sync (free for up to a certain amount of backed up data per month, after that a one time fee for lifetime updates). I do one additional thing, and it's for third-party storage. So if you're dead set on cutting out a third-party, I understand. But here me out. If the data is encrypted on the third-party system, it's largely a non-risk in terms of privacy unless your filenames themselves put your privacy at risk. I am fine with my filenames being seen, but the content being encrypted. So what I do is use Boxcryptor to encrypt the "destination" drive and then I use pCloud as my third-party storage provider. Both pCloud and Boxcryptor show up as physical drives on your computer, which I find convenient. So I have my primary source drive synced with the Boxcryptor drive/location and Boxcryptor is set up on my machine to encrypt the data on the fly as it is copied (surprisingly, this is not the default setting). Then, The pCloud software is set up to automatically sync that Boxcryptor directory where the files show in their encrypted format (the "drive" version shows them unencrypted because everything is done on the fly both ways) to my pCloud storage. In the end, I have 3 versions - the unencrypted source, the encrypted Boxcryptor copy, and the pCloud backup which contains the encrypted copy. Also important to note - pCloud is based in Germany and thus subject to the EU data protection laws and even without that I find pCloud to be a much lesser risk in terms of data privacy than any company in the US.