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.
For frequently changing data hourly up to 24, daily up to 7, weekly upto 4, monthly up to 12.
For daily changing data daily up to 7 and etc. as above.
For seldom changing data a backup every 3 days with rotation based on a storage quota, and retention of manually held samples.