Man… thanks! You are a really Master! It is not clear to me the further steps after the snapraid activities but I have to read it with more attention, I think.

Interesting, I will go deep. I think I should add or reformulate the question or I am missing a thing: I first have to avoid - or check - that source files are not bitrotten, otherwise all backups will be have bitrotten data, right? I mean, I might checksum but on working data how can I have evidence of it? And on “cold” data - f.e., pictures - how can be sure that source ruined files are not copied onto the backups? I cant - because of time - checksum 1tb of data every night…

And there is a best practise to do so … ?