GPFS already supports 2^64 files in a filesystem, and has been tested with 9 billion already. (2^64 is about 9 quintillion)
Use HSM and the policy engine and you can seamlessly migrate to and from tape (or anything else TSM supports for backend storage, which is just about everything).
http://publib.boulder.ibm.com/infocenter/clresctr/vxrx/index.jsp?topic=%2Fcom.ibm.cluster.gpfs.doc%2Fgpfs_faqs%2Fgpfsclustersfaq.html