Disk replication or SAN to SAN replication, replicates or move the saved data on disk to a different location. The problem with this is, that database engines like MS-SQL keep open transactions on memory. So if that's not taken into consideration, when you attach the database or files on the remote location, you may end with corrupted or broken databases.

Log Shipping solves that because it is basically replicating everything, including transactions. It does that moving transactions over the network and applying that on the remote SQL server.

With Veritas Cluster, you can actually combine both. You deploy SQL server using Veritas (one local one remote) but you use SAN to SAN replication as well.