SF gives redundancy for storage at a local site - i.e for failure of disks (or usually arrays), FC switches & HBA cards, by giving you mirroring and Disk Multipathing.
SFHA adds VCS (Veritas Cluster Server) which gives redundancy for servers on a local site - ie for failure of Server hardware, O/S or applications by monitoring servers (heartbeating) and applications). It does also protect againt network failures (switch and NICs), although most of this work is often done by the O/S with NIC bonding and similar technology's.
SFHA/DR extends on SFHA to give redundancy of servers across sites and controls data replication for the protection of your data across sites so you can control hardware replication such as SRDF and HTC, database replication such as Oracle Dataguard, or VVR (Veritas Volume Replicator) which is an extention of SF which gives replication of data over IP.
Mike
