As part of the cleanup process, old backups will be deleted. But how does the package determine whether a backup is "old".
This package provides an opinionated method to determine which old backups should be deleted. We call this the DefaultStrategy. This is how it works.
Rule #1: it will never delete the latest backup regardless of its size or age
Rule #2: it will keep all backups for the number of days specified in keep_all_backups_for_days
Rule #3: it will only keep daily backups for the number of days specified in keep_daily_backups_for_days for all backups older than those covered by rule #2
Rule #4: it will only keep weekly backups for the number of months specified in keep_weekly_backups_for_weeks for all backups older than those covered by rule #3
Rule #5: it will only keep weekly backups for the number of months specified in keep_monthly_backups_for_months for all backups older than those covered by rule #4
Rule #6: it'll only keep yearly backups for the number of years specified in keep_yearly_backups_for_years for all backups older than those covered by rule #5
Rule #7: it will start deleting old backups until the volume of storage used is lower than the amount specified in delete_oldest_backups_when_using_more_megabytes_than.
Those keep-* and delete_oldest_backups_when_using_more_megabytes_than attributes are present on the source and on the destination of backup and in the cleanup.default_strategy key of the backup-server config file.
First, cleanup process will try if the attribute is filled on the source, if not, it will look on the destination. When it's not filled in the destination it will use the value in the config file.