How exactly does your existing system fail over between datacenters without users noticing?
Surely they access that server via an IP address somewhere? So when a DC dies how does a drdb setup suddenly get that IP range announced from the DR datacenter?
Be careful how much your network relies on. Plenty of people here have found out the hard way that when a major DC goes down, so to do a lot of network operators and suddenly you can't even access the DR DC.
Anyway, the answer to your question is that most SANs have replication abilities. Or, you can use two unrelated SANs and VMware's replication software.