>Could anybody explain me why I consistently see "backup stg" jobs
>"freezing" ? What happens is that the job begins, but thereafter hangs
>for a while, doing nothing at all, and suddenly starts copying data on
>tape.  ...

A common cause is tape defects or un-cleaned drives which make for
time-consuming retries in reading the input tape or writing the
output tape.

  Richard Sims, BU