runspercycle does not need to be changed.  The "runtapes" means that
for each run up to that number of tapes may be used (note: not "must").

You have to increase your tapecycle probably to cover the same dumpcycle(s), because you'll burn twice as much tapes for each run.

(well, "burn", hopefully not litteraly).

I'm still not sure I understand. If I have

runspercycle 2

and

runtapes 2

will amanda try to distribute the full dumps across 4 tapes, or just 2?

When I think about it, the first answer makes most sense, as the parameter otherwise ought to have been called "tapespercycle".

"Sense" is a funny thing.

Amanda will "try" to fit each run on a single tape.  But will use a
second tape during that run if necessary.

 Thus the answer is "it depends".
It will try to use 2 tapes, but may use 3 or 4.

BTW I find it strange that an "archival" configuration would be setup with
a dumpcycle > 0 (or 1?) and with runspercycle > 1.

When I want an archive dump I want it to be the state of the system now.
Not the current state of half the DLE's and incrementals from the last
'archive' of the other half.  Maybe that is just me ;)

- Toralf