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New technologies for application recovery
Recent developments have bolstered a new high-availability computing model that comes closer to managing applications for continuity, rather than just very rapid recovery.
Transactional replication. As opposed to traditional replication, transactional replication creates a logical copy of the application and allows the target server to be in a hot standby mode. Because the target server is application-aware, certain integrity checks for physical and logical corruption can be performed as transactions are applied on the target. This ensures that if a transaction commits on the target, it's a valid transaction with valid data. Because it's a form of replication, transactional replication requires the shared-nothing disk model discussed earlier.
Transactional replication is available for most major relational database management products, as well as for the major messaging products. These capabilities are accessible through external APIs and can be easily leveraged by third parties to create high-availability
Shadow server. Running an active copy of an application on a target server has a variety of positive implications. First, because the application is already running, application recovery times are very short (measured in seconds for local configurations and minutes for remote ones). Second, as the source and target are kept in sync through replication, data RPO is very good; given that data is checked for corruption as it's applied, it's as good as can be operationally achieved with continuous data protection products. Third, because the shadow server is hosting a logical copy of the application, a variety of recurring activities like backup, archiving or data mining can be offloaded from the source to the target. Fourth, the shadow server can be used to handle any form of maintenance without impacting the source. Patches can be applied and validated first on the shadow server, ensuring higher quality in ongoing maintenance operations. In addition, the shadow server can be used to minimize downtime associated with any planned maintenance operations.
This was first published in April 2008