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 maintenance of two separate data sets with overlap in scope, either because of servers in a network design, or a failure condition based on servers not communicating and unifying their data to each other.

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. For example the split-brain syndrome may occur when all of the private links go down simultaneously, but the cluster nodes are still running, each one believing they are the only one running. The data set of each cluster then randomly may serve clients by their own "idiosyncratic" data set updates, without the coordination with the other data sets.

A shared storage may experience data corruption. If the data storages are kept separate data inconsistencies that might require operator intervention and cleanup.

To prevent the split-brain syndrom, 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.