[snip]
> Now, is there a way to do something like this with Amanda, a 
> way to define 
> set groups like this via different configs and share the same pool of 
> tapes?  Is there a way where I can indeed tell Amanda '30G of 
> people to 
> backup, do only 10G a day, but make sure every one is backed 
> up at least 
> twice in one week'?

I really don't think you need multiple configs, since you want to share
tapes. 

I'd do it in one config. Tell the users that their machines will be backed
up, at least in part, every night. An advantage of doing this is that if a
user misses a night when they should have had a full backup, they'll get one
the next night _automatically_. Full backups will be spread over the three
days to keep the run time and tape usage consistent. Letting AMANDA do her
job really is better.

amanda.conf:

# Change this to the number of tapes you want to cycle through:
tapecycle 6
# Full backups at least every three runs:
dumpcycle 3
runspercycle 3
# One tape per run:
runtapes 1

If you only want to use 10Gb of a 12Gb tape, change the tapetype to reflect
that. Or leave it at the tested capacity.

Add a machine or two a night. Check the run times to make sure they're not
colliding with normal use time. If the tape is slow, using a big holding
disk and boosting the "inparallel" setting can let the dumps finish quickly,
then take their time going to tape.