Currently the only solution for a consumer are M-Disc Blue rays. They are currently the only "write once read many" media available that are preferable in these types of situations.

The media is comparable cheap - you can safe your amount of data for around 80-90USD/€ initially(or less for more but smaller discs) and then pay around 10$/€ per year for the new amount of data.

The chances that in 20 years someone is still able to read them are fairly high - there are numerous businesses that are using these disc as WORM media to backup important data on a medium that a opposing lawyer later cannot claim "was manipulated". In 50 years it is very likely to be readable at least by professionals. The discs itself are rated for much longer storage.

If you write on them unencrypted there should be no problem of writing on them. Additionally they do not have issues with byte rot,etc.

Don't use them, but these seem right for you: https://lemm.ee/post/55012343

I decided instead to use ZFS. Better protection than just letting something sit there. Your backups are only as good as your restores. So, if you are not testing your restores, those backups may be useless anyway.

ZFS with snapshots, replicated to another ZFS box. The replicated data also stores the snapshots and they are read-only. I have snapshots running every hour.

I have full confidence that my data is safe and recoverable.

With that said, you could always use M-disk.

For local backups it depends on what you want to have:

• The cheapest option is a usb or thumb drive. But you have to regularly plug it in and copy your backup on it.
• The lazy option is to buy a NAS and configure a backup job that regularly creates a backup. Versioned, incremental, differentials and full backups are possible as is WORM to add a bit of extra security. You can configure a NAS to only turn on specified times, do a backup and then turn off again. This will increase protection against encrypting malware. WORM also helps in this case.
  Or just let it run 24/7, create backups every hour and install extra services on it like AI powered image analysis to identify people and objects and let it automatically tag your photos. Cool stuff! Check out QNAP and Synology or build a NAS yourself.
  A NAS can also be configured to present its content in a LAN by itself. Any computer will automatically connect to it if the access isn't secured by user/password or certificate.

I recommend buying a NAS.

I'm using blu-ray disks for the 3rd copy, but I'm not backing up nearly as much data as you are.

The only problem with optical media is that you should only expect it to be readable for a couple of years, best case, at this point and probably not even that as the tier 1 guys all stop making it and you're left with the dregs.

You almost certainly want some sort of tape option, assuming you want long retention periods and are only likely to add incremental changes to a large dataset.

Edit: I know there's longer-life archival optical media, but for what that costs, uh, you want tape if at all possible.

Just a hdd in usb caddy? IMHO good enough for 4 tier backup.

I have not used them myself, but M-DISC sounds like what you’re looking for. There are a few other alternatives listed on that Wikipedia article, too.

This was a recent point of discussion on the 2.5 Admins podcast (https://2.5admins.com/2-5-admins-228/). Some good discussion on there.

My own thought is the best way to handle your family-member-finding-your-old-photos problem is the analog way: make some prints. It’s absolutely idiot proof, the methodology of keeping paper goods is well understood, and the technology is platform independent.

The other thing is if I get hit by a bus and no one can work out how to decrypt a backup or whatever.

Documentation, documentation, documentation. No matter what system you have, make sure your loved ones have a detailed, image-heavy, easy to follow guide on how restorations work - at the file level, at the VM level, at whatever level you are using.

That being said, DVDs actually have quite a short shelf life, all things considered. I'd be more inclined to use a pair of archival strength USB NVME drive, updated and tested routinely(quarterly, yearly, whatever makes sense). Or even an LTO tape, if you want to purchase the drive and some tapes.

You can put your backups in something like VeraCrypt. Set an insanely long password, encoded in a QR code, printed on paper. Store it in the same secured location you store your USB drives (or elsewhere, if you have a security posture).

You may also consider, if money is not a concern, a cloud VPS or other online file storage, similarly encrypted. This can provide an easy URL to access for the less tech-savvy, along with secured credentials for recovery efforts. Depending on what your successors might need to access, this could be a very straightforward way to log into a website and download what they need in an emergency.