IBM DB2 Mirror for i - How does it work?

DB2 Mirror for i provides IBM i users with continuous availability of DB2. Ideal for organisations where downtime is not an option.

IBM believe they have changed the landscape of IBM i availability solutions with their brand new Db2 Mirror for i product. In the IBM i world, it provides a revolutionary HA solution which combines the best of hardware and software based replication technologies delivered as a new IBM Licensed Program. This article will point you to the considerations and decisions to be made if you want to get there.

High Availability can be categorised by the status of the target system in a replication pair. IBM categorise Db2 Mirror for i as the first genuine ‘active-active’ solution for application availability – it synchronously writes application data to two IBM i partitions on different servers. They describe their Power HA technology as ‘active-passive’ as it requires an application restart on the target system to complete the failover. Software based replication products such as market leader MIMIX from Syncsort also fit into the ‘active-passive’ category. In the case of full system disk based replication then an OS restart as well as application restart is also required.

IBM’s initial design remit for Db2 Mirror for i was to address a requirement of many of their high end enterprise customers who desire a zero RTO (Recovery Time Objective – the time it takes to failover). The simplicity and ease of use of the solution delivered actually makes it suitable for virtually all IBM i customers on current releases and current hardware. 

High-Level, how does it work?

You have two servers connected by high-speed Ethernet and an IBM i partition on each server. Db2 Mirror for i ensures application data is written to both servers synchronously across the high-speed Ethernet link. You decide which user libraries to include in replication. Data is available on both servers simultaneously but is read-only on one server. In a failover scenario data is already available on the target system and writes are seamlessly switched to the target system. To move to a genuine active-active environment all you need to do is front your application so it can talk to either server and system loss no longer results in application downtime.

The OS is not included and is managed separately on the source and target partition. The benefit here being you can switch replication in order to patch and upgrade one side of the replication pair and switch without application downtime.

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