All the data is spread across more than 3 sites, both SSDs and Blu-ray (which is immutable). I don't test the SSDs because I trust Rclone, the Blu-ray is only tested after writing.
There is surely risk of Bit rot on the SSDs but it's out of sight and out of mind for my use case.
I've been considering to get in to the Blu-ray backups for a while. Is there a good guide on how to organize your files in order to split it in to multiple backup disks? And how to catalogue all your physical Discs to keep track of them?
I remember about 20 years ago my friend had a huge catalogue of 100s of disks with media(anime) and he used some kind of application to keep track of where each file is located across 100s of discs in his collection. I assume that software must have improved for that sort of a thing?
I don't know about the best way to split things (I do it topically mostly, e.g. each website backup goes to a separate disc). But hashdeep is a great little tool for producing files full of checksums of all files that get written to the disc, and also for auditing those checksum files.
There is surely risk of Bit rot on the SSDs but it's out of sight and out of mind for my use case.