IBM SG24-5131-00 manual Rotating Standby Configuration, Hot-Standby Configuration

Figure 2. Hot-Standby Configuration

In this configuration, there is one cascading resource group consisting of the four disks, hdisk1 to hdisk4, and their constituent volume groups and file systems. Node 1 has a priority of 1 for this resource group while node 2 has a priority of 2. During normal operations, node 1 provides all critical services to end users. Node 2 may be idle or may be providing non-critical services, and hence is referred to as a hot-standby node. When node 1 fails or has to leave the cluster for a scheduled outage, node 2 acquires the resource group and starts providing the critical services.

The advantage of this type of a configuration is that you can shift from a single-system environment to an HACMP cluster at a low cost by adding a less powerful processor. Of course, this assumes that you are willing to accept a lower level of performance in a failover situation. This is a trade-off that you will have to make between availability, performance, and cost.

Rotating Standby Configuration

This configuration is the same as the previous configuration except that the resource groups used are rotating resource groups.

In the hot-standby configuration, when node 1 reintegrates into the cluster, it takes back the resource group since it has the highest priority for it. This implies a break in service to the end users during reintegration.

If the cluster is using rotating resource groups, reintegrating nodes do not reacquire any of the resource groups. A failed node that recovers and rejoins

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