Hi Gilbert,
I find myself wishing I had a bit more control of granularity over snapshot retention with the prune command. I do hourly backups for some particularly sensitive and fast-changing files and would like the ability to define a retention policy that deals with hours. Currently prune’s -keep is hardcoded to days.
Moreover, it can sometimes be difficult to reason about how a particular policy will actually materialize over time, because the more recent retention periods dictate what will be rolled up to the further out periods.
Some time ago, I wrote a simple tool to manage droplet snapshots for Digital Ocean and my implementation for retention was heavily inspired by duplicacy, but I believe I improved on it in two ways:
- Intervals and durations take a time unit, so you can describe either (and independently) in hours, days, weeks, and months
- there is a
--simulateoption that runs a simulation of how your retention policy will look after a given period (where you describe how frequently you run the backup and how over how many times). This helps you spot stupid mistakes in your retention policy before actually implementing.
I think it’d be cool if duplicacy implemented either or both of these ideas (but especially #1 
).
Thanks!