split brain
also: cluster split, partition failure
A state where a distributed system splits into isolated partitions that can no longer communicate, each partition believing it has authority or is the primary node.
Split brain occurs in clustered or distributed Linux systems (such as database clusters, high-availability pairs, or distributed storage) when network communication fails between nodes, causing each isolated partition to operate independently and potentially make conflicting decisions.
Each partition may believe it is the legitimate primary or master, leading to data inconsistency, conflicting writes, or duplicate resource allocation. For example, in a two-node HA cluster with shared storage, if the network link fails, both nodes may try to become the active node and write conflicting data.
Prevention mechanisms include quorum-based voting (requiring a majority of nodes to agree), fencing (forcibly shutting down minority partitions), and heartbeat monitoring with STONITH (Shoot The Other Node In The Head) to ensure only one partition can proceed.