I am trying to create a staging backup scenario where the primary's backups are wriiten to disk and then copied to 3rd tier disk setup (long term) and finally tape. Was reading up on duplication, Vault and storage life cycle policies but confused on what to use. I would also like not to have too stage the restores to regain a sinfgle file from an image.
If your intent is merely to stage the backup, then you are better off using the DSSU [Disk staging storage unit] in NBU. Using DSSU, you can stage the backups to a disk storage unit and subseqently [i.e post backup] , the backup image is moved to the disk/tape.
If you want to define differential retention periods for each of the stages, Storage lifecycle policies are to be used. With this you have a control on how long the backup images are stored on each tier planned unlike in DSSU
Duplication and Vault address only a part of your requirement. Hence not recommeded.