{
  "status": "shipping",
  "advantages": [],
  "limitations": [
    {
      "text": "Successful fencing prevents further conflicting access within its enforced scope but does not reconcile writes already accepted.",
      "citationIds": [
        "pacemaker",
        "drbd-split-brain"
      ]
    }
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-11-09",
  "slug": "split-brain",
  "term": "Split brain",
  "aliases": [
    "Split-brain"
  ],
  "definition": "Split brain is a clustered-system failure state in which nodes unable to coordinate independently operate a resource that requires coordinated access.",
  "note": "Scope: A network partition describes lost communication; split brain describes a resource-control failure that can accompany it. Coordinated multi-writer operation is not itself split brain. [pacemaker]\n\nRecovery: DRBD distinguishes a partition from disconnected primary roles and divergent data histories. A reconnection handshake can detect split brain and drop replication. Recovery policies may select a surviving copy and discard changes on the other side, not merge application updates. [drbd-split-brain]\n\nPolicy selection: The after-sb-0pri, after-sb-1pri and after-sb-2pri options distinguish primary-role counts at detection. They do not count the nodes that accepted writes during the disconnection. Therefore, a current Secondary role does not by itself establish that discarding that copy loses no updates. [drbd-split-brain]",
  "related": [
    "network-partition",
    "io-fencing",
    "fencing-token",
    "quorum-intersection",
    "shared-disk-filesystem"
  ],
  "citations": [
    {
      "id": "pacemaker",
      "title": "ClusterLabs: Pacemaker Explained 3.0, Fencing, sections 8.1-8.3 and 8.11",
      "url": "https://clusterlabs.org/projects/pacemaker/doc/3.0/Pacemaker_Explained/html/fencing.html",
      "accessed": "2026-11-09"
    },
    {
      "id": "drbd-split-brain",
      "title": "LINBIT: DRBD 9 User Guide, split brain notification, recovery policies and manual recovery",
      "url": "https://linbit.com/drbd-user-guide/drbd-guide-9_0-en/",
      "accessed": "2026-11-09"
    }
  ],
  "provenance": [
    "DRBD 9 guide sections 2.12, 5.19.2 and 7.5 describe implementation-specific detection and recovery, not a universal definition or a tested failover procedure."
  ]
}