ZFS is a new kind of file system that provides simple administration, transactional semantics, end-to-end data integrity, and immense scalability. ZFS is not an incremental improvement to existing technology; it is a fundamentally new approach to data management. We've blown away 20 years of obsolete assumptions, eliminated complexity at the source, and created a storage system that's actually a pleasure to use.

http://www.opensolaris.org/os/community/zfs/whatis/;jsessionid=98484C5664C60A7B643F5E9C78165517