Home > RAC > Split Brain Syndrome and I/O Fencing (RAC).

Split Brain Syndrome and I/O Fencing (RAC).

January 18, 2014

Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect, Although the servers are physically up and running and the database instances on these servers is also running.

The individual nodes are running fine and can accept user connections and work independently.

So, in a two node situation both the instances will think that the other instance is down because of lack of connection.

The problem which could arise out of this situation is that the sane block might get read, updated in these individual instances which cause data integrity issues, because the block changed in one instance will not be locked and could be overwritten by another instance.

So, when a node fails, the failed node is prevented from accessing all the shared disk devices and groups. This methodology is called I/O Fencing, Disk Fencing or Failure Fencing.

In a RAC environment the node which first detects the other unreachable node will evict it from the cluster to avoid data corruption.

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Categories: RAC
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