I agree. GP comment brings to mind the infamous reply to Dropbox Show HN which compared it to something users could trivially implement using basic Unix commands.

I add files to the new drive throughout the year. I keep the drive unplugged most of the time but periodically plug it in to add files. I still have a >1 year recovery point in case of fire, but less than that for more mundane data loss scenarios (accidental deletion, etc).

I have more than one backup drive, and rotate them. I just protect myself against aging drive failure by rotating in a new one once in a while.

1. buy the drive

2. plug it into my system via a USB drive adapter

3. format the drive

4. run the program I wrote to copy the files I want to back up to it

5. unplug the drive

6. plug the drive in next time I want to do a backup

7. run my program again, which will only copy over changed files. You could use rsync if you prefer

8. unplug the drive

Error modes? I've had disk drives fail now and then. I have a 10 lb sledge hammer I use to render it unreadable by anyone but the NSA, and throw it in the trash. Buy another one.

I suppose I'm not really understanding your question. But it really is this low tech and simple.