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High Availability on System p

Will live partition mobility replace IBM's flagship availability product on the midrange, IBM's High Availability Cluster Multi-Processing (HACMP)? The answer is no.

 

Each resource is defined as being part of a resource group, which are then configured to have relationships with its nodes. Depending on this relationship, resources can be defined in four different ways: cascading, cascading without fallback, rotating or concurrent access. When the primary server goes down because of a failover event, the HACMP software on the standby system recognizes this event and starts to take action, usually taking over the service IP address of the primary policy server. The HACMP software will also mount the shared filesystem on the standby system and start up its applications.

In a typical cascade relationship, the standby server remains operational until the HACMP software on the standby system recognizes that the primary system is operational and falls back. In this relationship, one would plan for when they want to run the application again on the primary server. While you can theoretically have both hosts function as logical partitions on one System p frame, that would defeat the purpose of having hardware availability, so let’s assume these partitions are on two separate frames. It’s also important to note that in the event that the standby server is configured to backup several primary servers, the failover node must be configured to be able to service all available workloads. Note that because the disk is shared, HACMP doesn’t provide for disk availability. Your storage subsystem must provide for that level of redundancy.

Testing your HACMP is one of the most important components of an HACMP deployment. Before deploying HACMP in production, every possible scenario should be tested to ensure that the cluster works the way it was designed to work. When validating that testing, it’s not enough for your UNIX administrators to say that it works. Functional applications teams must be part of the HACMP validation process or else it really hasn’t been tested adequately. The purpose of HACMP isn’t so much to ensure that filesystems or processes have started on another box, but that every application you’ve identified must continue to work in the event of a failover and works without any manual intervention.

 

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