If you’re relying on one hard drive not failing to preserve your data you are doing it wrong from the jump. I’ve got about a dozen hard drives in play from seagate and WD at any given time (mostly seagate because they’re cheaper and I don’t need speed either) and haven’t had a failure yet. Backblaze used to publish stats about the hard drives they use, not sure if they still do but that would give you some data to go off.