When submitting questions on restoral issues, always provide details
on what was done in the restoral attempt, as the approach and elements
involved can greatly affect results.  We also don't know your TSM
level: assure that you have recent maintenance applied, in order to
eliminate any known impairments.

Go to the TSM Support Page and search on:
  ndmp restore performance

That will turn up Technotes such as 1240077, which may help you
evaluate what you are experiencing relative to the approach used.
Beyond that, you may have to perform some analysis there to uncover
any incidental performance issues, such as network configuration
problems or the tape drive struggling to read the tape due to media
problems.

   Richard Sims