Every Disaster Recovery Plan involves the backup and restore capability of data. Far too often, there is is not enough thought given to data retention policies. Sure, you might be backing up your data every day on three weeks rotation of separate tapes, taking them off-site and other steps to be safe. But what happens if you need to restore something that was deleted two or three months earlier and you just now discovered the data was missing? In this case, the deleted data would reside on tapes that have already been overwritten by other backup jobs.
Be sure to carefully think through your backup data retention policy. Better yet, have an experienced third-party consultant help you with this to ensure the bases are covered.