Right now I’m creating a nightly restic snapshot of my server on borgbase and on some spare drives, and keeping the snapshots forever. There’s a ton of daily churn in my data though, between databases and logs and other files that don’t constitute ‘real data’ but might be needed to restore the app.
As of now, i keep them basically for ever, but granularity gets less over time. (restic forget)
Before you go nuts about files you want to exculde the “churn” as you said it, go ahead and actually check how much space this actually takes up. Text and especially logs are highly compressible and will most likely end up taking up almost no space.
Be sure you backup everything you actually need, rather backup a file more then a file too less.
Comparing daily snapshots I see 100mb+ daily churn (I assume restic diff is pre compression), the borgbase repository space usage chart shows it increasing about 50mb daily.