K, now that I've solved (thanks to everyone here's help) the problem of
having disks that are larger than my tape's capacity. I think I better add
tapes to my existing system. here's what I've got in Amanda.conf relative
to this now:

dumpcycle 5 days        # the number of days in the normal dump cycle
runspercycle 5          # Number of time Amanda will be run per dump cycle
tapecycle 20 tapes      # the number of tapes in rotation

What's the safest way (where safe is defined as not risking availability of
my existing backups) to add more tapes, without taking the ones I have out
of service. Let's say I want to go to 40 tapes.

Yes, Amanda is run _every_ day, as the above implies, this is my home
setup.

I may also have to increase dumpcycle, but I won't know that until I've run
a few days to get the balance back.

-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
                                                -- Benjamin Franklin