>But will this export (write) all data to a new set of tapes

In colloquial terms, Export spews: all the data is written, to new tapes, in
portable form, and it takes time to do this, as in one large filespace taking
basically all day.  Then you have to keep track of what tape has what, and
later get it all straight in doing an Import.  Those who have done it dread
doing it again.  If you do Export, scrutinize the resultant Activity Log
messages VERY carefully.  It can happen that Export fails to write data, but
takes so long that you feel confident that it did.
     Richard Sims, BU