Active/passive vs active /active Cluster

Active/Passive

An active/passive cluster generally contain two identical nodes.At any time, one of the nodes is active and the other is passive.Oracle singel instance database software is installed on both nodes, but the database is located on shared storage.During normal operation, the Oracle database instance runs only on the active node.In the event of a failure of the currently active primary system,clustering software will transfer control of the disk subsystem to the secondary system, a process known as failover.As part of the failover process, the Oracle instance on the secondary nose is started, thereby recovering and resuming the service of the Oracle database. All connections to the instance on the primary system at the time of failure are terminated and must be reestablished withe the new instance on the secondary system.On resolution of the issue, the Oracle instance is cleanly shut down on the secondary system , control of the disk subsystem is transfered back to the primary system and oracle instance is started to resume normal operations.

a number of third party products are avilable to implement active /passive clustering on linux.

Active/Active

An active /active cluster has an identical hardware infrastruture to an active /passive one. However, Oracle instances run concurrenlty on both servers and access the same database. which is located on shared storage. The instances must communicated with each other to negotiate access to shared data in the database. In the event of a server failure, the remaining server can continue processing the workload and optionally failed sessions can be reconnected . the benefit of an active / active cluster over an active/passive cluster is that,during normal processing, the workload can be shared across both servers in the cluster

Oracle RAC is desighned to run in an active / active enviornment.