The following examples illustrate using spare nodes in HADB deployments. There are two possible deployment topologies: co-located, in which HADB and Application Servers reside on the same hosts, and separate tier , in which they reside on separate hosts. For more information on deployment topologies, see Chapter 3, Selecting a Topology
As an example of a spare node configuration, suppose you have a co-located topology with four Sun FireTM V480 servers, where each server has one Application Server instance and two HADB data nodes.
For spare nodes, allocate two more servers (one machine per DRU). Each spare machine runs one application server instance and two spare HADB nodes.
Suppose you have a separate-tier topology where the HADB tier has two Sun FireTM 280R servers, each running two HADB data nodes. To maintain this system at full capacity, even if one machine becomes unavailable, configure one spare machine for the Application Server instances tier and one spare machine for the HADB tier.
The spare machine for the Application Server instances tier must have as many instances as the other machines in the Application Server instances tier. Similarly, the spare machine for the HADB tier must have as many HADB nodes as the other machines in the HADB tier.