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Microsoft SQL Server 2008 R2 Unleashed- P238

Microsoft SQL Server 2008 R2 Unleashed- P238:SQL Server 2005 provided a number of significant new features and enhancements over what was available in SQL Server 2000. This is not too surprising considering there was a five-year gap between these major releases.Microsoft SQL Server 2008 is not as much of a quantum leap forward from SQL Server 2005 | 2334 CHAPTER 56 SQL Server Disaster Recovery Planning A few things may cause issues for this pattern such as the need to make sure that no application keeps state from one transaction to the other. Additionally the application and or the web tier needs to be able to route user connections the load to either site in some type of balanced or round-robin method. This is often done with big IP routers that use round-robin routing algorithms for example to determine which site to direct connections to. Active active configurations can be created using peer-to-peer continuous data replication as well as other multi-updating subscriber replication topologies. A slight twist to having two primary sites is to have one primary site and a secondary site that doesn t process transactions but is actively used for reporting testing and other tasks just no processing that changes anything . In the event of a primary failure the secondary site can take over full primary site responsibilities quickly. This is sort of active passive with active secondary usage on the passive site following the first active passive DR pattern described previously . This type of configuration can take advantage of database mirroring and database snapshots for the reporting . There are plenty of advantages to this variation which greatly distributes the workload and moves up the DR pyramid. Active Multisite DR Pattern An active multisite DR configuration contains three or more active sites with the intention of using any one of them as the DR site for the other as shown in Figure 56.4 . This pattern allows you to distribute your applications redundantly between any pair of sites but not to all three or more . For instance you could have half of Primary Site 1 s applications on Primary Site 2 and the other half on Primary Site 3. This way you spread out the risk further and increase your odds of uninterrupted processing. Again having stateless applications is critical here as is some smart routing of .