You might want to check with your SAN vendor. I know that EMC, IBM, HP and Dell all have some type of SAN to SAN level replication but those usually require you have the same SAN on both sides. In full disclosure I work for Double-Take software which is host based replication, at the byte level, but runs on the Exchange server host replicating the data in real-time that resides on the SAN. I think EMC has snapmirror, IBM has a level of replication with their DS3000, Dell has Equallogic and HP has storage works storage mirroring. You will probably need to evaluate what works best for the SAN you have becuase not all SAN replication products will likely be supported depending on the vendor.
- hope that helps