TSM & Retention Policies
If you've managed a backup solution before (DPM, BackupExec, UVB, Veamm, etc.), then retention was probably set by answering the simple question of "How long do I want to keep this stuff for?" Most of the time, retention is a simple setting. Set it & forget it right? in Tivoli Storage Manager, or TSM, it's a bit more complex than that.