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Oracle10g Grid Computing with RAC
Chapter 3 - High Performance and Highly Available
Database Clusters

Avoiding Split Brain 

Split Brain Condition occurs when a single cluster has a failure that results in reconfiguration of cluster into multiple partitions, with each partition forming its own sub-cluster without the knowledge of the existence of other. This would lead to collision and corruption of shared data as each sub-cluster assumes ownership of shared data.

As an example, when two systems have access to the shared storage, integrity of the data depends on the systems communication through heartbeats using the private interconnects. When the private links are lost and failed or if one of the systems is hung or too busy to send / receive heartbeats, each system thinks other system has exited cluster, then it tries to become master (or form a sub-cluster) and claims exclusive access to the shared storage. This condition leads to Split Brain.

There are definite methods (or fencing) to avoid such a tricky and undesirable situation. There are two basic approaches to fencing: resource based fencing, and system reset (or STOMITH or STONITH) fencing.

Resource-based fencing includes IO fencing and the maintenance of Quorum disks. In resource-based fencing, a hardware mechanism is employed, which immediately disables or disallows access to shared resources. If the shared resource is a SCSI disk or disk array, one can use SCSI reserve/release (or better yet persistent reserve/release operations). If the shared resource is a fiber channel disk or disk array, then one can instruct a fiber channel switch to deny the problem node access to shared resources. In general, the errant node itself is left undisturbed, and its resources are instructed to deny access to it. If the node is able to later become part of a cluster with quorum, it will then go through the normal channels to reacquire its resources.

For more information, see the book Oracle 11g Grid and Real Application Clusters 30% off if you buy it directly from Rampant TechPress . 

Written by top Oracle experts, this RAC book has a complete online code depot with ready to use RAC scripts.

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Burleson Oracle Consulting offers Senior Oracle consultants which are available for all areas of Oracle support.  Common Oracle consulting support activities include short-term Oracle tuning, Oracle database troubleshooting, Oracle9i and Oracle10g migration, Oracle9iAS App Server consulting, Oracle design reviews and Oracle requirements evaluation support. Oracle support and Oracle consulting services are priced by the hour, so you only pay for what you need. These one-time Oracle consulting services commonly include:

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