As perrin and crazyinsomniac mention you sound like you need a database.

I personally like postgres because its free, transaction based, and easy to setup and configure.

IMHO you will only have too much data when it starts to become irrevalent, for example, if you have a book in your catalogue, that you will never reference/gone out of print/has been stolen et al, perhaps you dont need that record.

If you start to constrain your data to fit your iron, you need another method of accessing it.