All I've ever done in these cases is use duplications to do what I wanted. The backup runs to the 1st storage unit (your 1st level disk) then duplicates to the 2nd storage unit (3rd tier disk) and the 3rd storage unit (tape), as needed. I would make the 3rd tier disk copy the primary copy after the duplication, to speed up restores (instead of tape). Storage lifecycle policies, from what I understand, can help you do that somewhat more automatically and leave you with the same basic thing. If you had servers for instance that fit into categories like R&D for one group, HR for another, etc, that you have different retentions and plans for, it can be easier to use SLPs to manage that, but I've never played around with them that much.
