Split-brain (computing)

Split-brain is a term in computer jargon, based on an analogy with the medical Split-brain syndrome. It indicates data inconsistencies originating from the mainenance of two separate data sets with overlap in scope, either because of the network design, or a failure condition based on servers not communicating and unifying their data to eachother.

Typical usage of the jargon term is when internal and external Domain Name Services (DNS) for a corporate network are not communicating, so that separate DNS name spaces are to be administrated for external computers and for internal ones. This requires a double administration, and if there is domain overlap in the computer names, there is a risk that the same fully qualified domain name (FQDN), may ambiguously occur in both name spaces referring to different computer IP addresses.

High-availability clusters usually use a heartbeat private network connection which is used to monitor the health and status of each node in the cluster. One subtle, but serious condition every clustering software must be able to handle is split-brain.

Split-brain occurs when all of the private links go down simultaneously, but the cluster nodes are still running.

If that happens, each node in the cluster may mistakenly decide that every other node has gone down and attempt to start services that other nodes are still running. Having duplicate instances of services may cause data corruption on the shared storage.

This problem can lead to data inconsistency. To prevent it computers should use redundant communications and fall down to an auto-fencing mode when the peers look like they are down. This means they should run in a limited mode to prevent data destruction