[dominicperry]

I forgot to mention - SSD isn't a very reliable long-term storage medium, unless you plug the disk in and let it "refresh" every six months or so. The charge in the cells fades away and suddenly the data gets corrupted.

I spent quite a long time researching this, and got nowhere. Well, I got to learn about SLC, MLC, TLC and QLC design and production, but I didn't get any definitive information about which kinds of SSD are most vulnerable to the problem, nor did I get to find out how long a "refresh" takes - I just plug the disk into my USB hub and mount the disk and leave it mounted for a couple of hours. I have no idea if it's necessary to read or re-write the data to refresh the charge state.
My main mitigation for this is have multiple other medium types (cloud and HDD) with the same data.

One more thing - all my backups are encrypted. And the encryption password is different for each one - my Tresorit password with MFA (multi-factor authentication) is different from my iDrive password (with email MFA), is different from my CCC encryption password. So make sure that if your primary data storage fails, you have a way to retrieve your encryption passwords. I thought the whole thing through once and realised that if my laptop and phone were stolen at the same time, I would never be able to get back into my 1Password vault (which is stored in Dropbox) and so I'd never be able to get into my email account, so I'd never be able to reset my Dropbox password, so I'd never get into my Dropbox account to get my password database, etc etc etc. I fixed this by changing my Dropbox password to something memorable rather than 26 characters of gobbledygook.

Dominic