Lotus Notes on AS400 – storage issues

We run Lotus Notes for about 200 users on a small AS/400 Model 170. It has 16 GB of useable storage and we are using 74% of it. Users don’t do well at archiving, nor do they want to get rid of anything. I’m thinking of getting more disk for the AS400 or a new AS400, or storing the users’ Notes databases on some sort of storage server if that is possible. Any advice would be appreciated.