Designing a Geographically Dispersed Cluster
Updated: March 28, 2003
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
Geographically dispersed server clusters ensure that a complete outage at one site does not cause a loss of access to the application being hosted. All nodes hosting an application must exist within the same cluster. Therefore, to provide fault tolerance, a single cluster spans multiple sites.
Windows Server 2003 supports two-site geographically dispersed clusters. However, Microsoft does not provide a software mechanism for replicating application data from one site to another. Instead, Microsoft works with hardware and software vendors to provide a complete solution. For more information about qualified clustering solutions, see the Windows Server Catalog link or the Geographically Dispersed Clusters link on the Web Resources page at http://www.microsoft.com/windows/reskits/webresources.
A geographically dispersed cluster requires multiple storage arrays, at least one in each site, to ensure that in the event of failure at one site, the remaining site will have local copies of the data. In addition, the nodes of a geographic cluster are connected to storage in such a way that when there is a failure at one site or a failure in communication between sites, the functioning nodes can still connect to storage at their own site. For example, in the simple two-site cluster configuration shown in Figure 7.23, the nodes in Site A are directly connected to the storage in Site A, so they can access data with no dependencies on Site B.
Figure 7.23 Geographically Dispersed Cluster
In Figure 7.23, Nodes A and B are connected to one array in Storage Controller A, while Node C and Node D are connected to another array in Storage Controller B. These storage arrays present a single view of the disks spanning both arrays. In other words, Disks A and B are combined into a single logical device (by using mirroring, either at the controller level or the host level). Logically, the arrays appear to be a single device that can fail over between Nodes A, B, C, and D.
For a job aid to assist you in gathering your requirements for a multisite server cluster and organizing the necessary, preparatory information, see "Planning Checklist for Geographically Dispersed Clusters" (Sdcclu_1.doc) on the Microsoft® Windows® Server 2003 Deployment Kit companion CD (or see "Planning Checklist for Geographically Dispersed Clusters" on the Web at http://www.microsoft.com/reskit).