I may be wrong but I think it is 300/500 passes over the tape. This
translates to 5/10 reads/writes.
(I'm getting paid by the slash today.) This was explained to me by someone
at the Response Center years ago. Since to read or write to a tape the tape
actually passes over the tape multiple times. This is most evident in 9
track drives back and forth movement. I would assume VSTORE also does
multiple passes.
I don't know how long it will last in years.