[rdiff-backup-users] max archive size / revision depth

[address@hidden]

Hi,
  I'm going to use rdiff-backup in order to save about 70Gb of files (!).
If I start to use it, probably after some mounths/years it will fill the hd: 
how can I "compact" it, deleting/compacting olds revisions of the files?

For example: I will delete an entire folder, but (I suppose) rdiff-backup will 
keep it in his backup-history.
If I will not restore that folder, probably after an year I will be sure we'll 
not need it anymore, so I can delete it form the history to free some space, 
right? How can I do it?

Thanks
Alessandro