Geographically dispersed (majority node set) server clusters are built on a networking and storage infrastructure with characteristics that are very different from a standard quorum device server cluster. Therefore, they are certified under a separate testing program. If you want to convert your existing server cluster to a geographically dispersed server cluster, work with your hardware vendor to obtain a geographically dispersed server cluster configuration that has been certified by Microsoft.

You can create many geographically distributed solutions by adding data-replication software and extended Local Area Network (LAN) hardware to existing certified configurations. However, these solutions radically change the nature of a precertified configuration, particularly with respect to timing and latency. Therefore, Microsoft requires that, for it to be supported by Microsoft, the hardware and software configuration of a geographically dispersed cluster be one that is certified and listed on the cluster Hardware Compatibility List (HCL). For additional information about the HCL and Windows Clustering, click the following article number to view the article in the Microsoft Knowledge Base: Nonqualified software solutions on existing signed hardware are not supported.

You can use Windows Clustering to implement geographically dispersed clusters in scenarios where you can deploy the members of a single cluster on several different sites. Windows Clustering does not detect the extended nature of these types of clusters, and it is the responsibility of the network and storage architectures that are used to build these geographic clusters to preserve the semantics. In particular:

• The private and public network connections between cluster nodes must appear as a single, non-routed LAN that uses technologies such as virtual LANs (VLANs). In these cases, the connections network must be able to provide a guaranteed, maximum round-trip latency between nodes of no more than 500 milliseconds. The Cluster Interconnect must appear as a standard LAN.
• Any geographically replicated storage technologies must preserve single disk semantics, such as persistent arbitration of a LUN-to-Windows Clustering. The quorum disk must be replicated in real-time, synchronous mode across all sites.

Because of the complexity of geographically separated clusters, you must involve the hardware manufacturer in any issue. Frequently, the configuration includes third-party software and drivers that are required for the clusters to function. Microsoft Product Support Services may not be aware of how these components interact with Windows Clustering.

Configurations must be certified with a maximum supported distance between nodes for a particular site interconnect (such as a certified configuration with nodes that are one mile apart that uses fiber that is not supported if the nodes are deployed more than one mile apart or if the interconnect is copper).

For additional information, visit the following Microsoft Web site: