||Oracle Tips by Burleson
Oracle10g Grid Computing
Chapter 3 - High
Performance and Highly Available
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
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.
Oracle Consulting Services
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:
Answering questions from your Oracle DBA technical staff
Repairing down production Oracle database systems
One-time Oracle tuning evaluation
Guru support for your Oracle DBA
Installation of Oracle application packages
For more information, please visit