air-gapped, offline, distributed backups
This is my strategy for ensuring data integrity.
My PC boots from a pair of SATA SSD's, the intermediary technology between spinning disks (HDD) and high-performance M.2-based storage that dispenses with the bottleneck created by the old SATA bus. SATA, now 25 years old, was designed primarily for the old spinning platter HDD storage of the late 20th Century. M.2 systems have about 6x-7x the bandwidth. I keep the operating system on the former but my working data on the latter. But I don't trust SSD due to a track record of failure of the disks. So I copy data here, there, and literally everywhere.
I have two 4TB HDD in the system that are always mounted. I use licensed software to manually copy the data from the M.2 SSD drive. I do this because I want to be sure that I'm not replicating accidental deletion of my files.
I have another pair of HDD, these being smaller 2TB HDD, in an inexpensive external enclosure. This I keep unplugged unless I am performing backups. This gives me a copy of my data that would survive things like a virus, a catastrophic electricty-based disaster, user error, and deliberate destruction by an intruder. The data I have somehow has expanded to almost fill these drives, so I tend to be vicious about which photos I retain in order to preserve this setup. By keeping these systems unplugged, I am maintaining an air-gapped, offline copy. I once again manually copy my files to these volumes.
But the external enclosure is heavy and bulky, and I live in Japan where the possibility of natural disaster is high. So I have a second external enclosure, even cheaper than the first one. It has a single 4TB drive in it, and is offline most of the time though plugged into the main system. This is my "go" disk; I have a plastic container for the lone 4TB drive kicking around the bedroom, and in case of an earthquake or fire I would take a few precious seconds to get the drive its container and then I'd carry it with me in my always-ready "go" bag or throw that out the window.
But what about off-site backups? Well, this is where venerable BR-D devices come in. Yes, I still use optical media. They are very reliable, even better than HDD, and I can store a set of my back-ups with my brother in Canada or my in-laws 1,000km away in southern Kyushu. These disks can be found in retail stores everywhere in Japan, and are very inexpensive.
The problem is, I tend to delay writing my files to optical disks, so I occasionally have a day like today where I spend the entire time writing nine month's data to disk. I'll do the same tomorrow, I suspect.