Building a geographically dispersed SQL Server cluster to host SharePoint relies on third-party applications to overcome the 'same subnet' limitation. A self-sufficient storage replication infrastructure that is outside the Microsoft product line also relies on third-party applications to overcome this limitation. These configurations are vendor-specific, so the SharePoint Product Group did not test them.
We do not offer end-to-end support for the kinds of configurations that are described in the "Introduction" section. We require users to eliminate the third-party component as a cause of the problem before we provide support. In certain cases, the customer would have to show a reproduction of the problem in a co-located environment.
Notes and caveats:
All active Servers in a farm should have a maximum of 1 millisecond latency to the SQL Server that serves them.
Planning and Monitoring SQL Server Storage for Office SharePoint Server: Performance Recommendations and Best Practices (white paper)
The following is the Microsoft general support policy when third-party clustering tools are involved:
"If you cluster SQL Server with any clustering product other than Microsoft Server Clustering, your primary support contact is the third-party cluster solution provider for any support issues that are related to SQL Server. SQL Server was developed and tested by using Microsoft Server Clustering. Third-party clustering solutions that support SQL Server installations should be your primary contact for any installation issues, performance issues, or cluster behavior issues. CSS provides commercially reasonable support for third-party cluster installations in the same manner that we do for a stand-alone version of SQL Server."
327518 The Microsoft SQL Server support policy for Microsoft Clustering
814607 Microsoft support for server clusters with third-party system components
Additional resources and recommended SharePoint topologies are available on the TechNet Center.
Backup, Recovery, and Availability Resource Center for SharePoint Server 2007