A variation of the separate tier topology is to increase the number of Application Server instances by adding more machines horizontally to the configuration. For example, add another machine to the example configuration by creating a new Application Server instance. Similarly, increase the number of HADB nodes by adding more machines to host HADB nodes. Recall you must add the HADB nodes in pairs with one node for each DRU.
Variation of Separate Tier Topology illustrates this configuration.
In this configuration, each machine hosting Application Server instances has two instances. There are thus a total of six Application Server instances in the cluster.
HADB nodes are on machines SYS3, SYS4, SYS5, and SYS6.
DRU0 comprises two machines:
SYS3, which hosts HADB node active 0 and HADB node active 2.
SYS5, with HADB node spare 4 and HADB node spare 6.
DRU1 comprises two machines:
SYS4, which hosts HADB node active 1 and HADB node active 3.
SYS6, which hosts HADB node spare 5 and HADB node spare 7.
Each machine hosting HADB nodes hosts two nodes. Thus, there are a total of eight HADB nodes: four active nodes and four spare nodes.