Merge policy A PowerHA merge policy defines the behavior of a cluster  when a cluster merge occurs. Quarantine policy A PowerHA quarantine policy defines how a standby node  isolates or  quarantines  an active node or partition from the  shared data to prevent data corruption when a cluster split  occurs. Critical resource group When multiple resource groups (RGs) are configured in a  cluster, the RG that is considered as most important or critical  to the user is defined as the critical RG for a quarantine policy.  For more information, see 9.3.1, “Active node halt quarantine  policy” on page 337. Standard cluster A standard cluster is a traditional PowerHA cluster. Stretched cluster A stretched cluster is a PowerHA V7 cluster with nodes that are  in sites within the same geographic location. All cluster nodes  are connected to the same active and backup repository disks  in a common storage area network (SAN). Linked cluster A linked cluster is a PowerHA V7 cluster with nodes that are in  sites in different geographic locations. Nodes in each site have  their own active and backup repository disks. The active  repository disks in the two sites are kept in sync by Cluster  Aware AIX (CAA). GLYPH<SM590000> None GLYPH<SM590000> Tiebreaker GLYPH<SM590000> IBM PowerHA SystemMirror for AIX Cookbook , SG24-7739 GLYPH<SM590000> IBM PowerHA SystemMirror V7.2 for IBM AIX Updates , SG24-8278 9.2 PowerHA cluster split and merge policies (before PowerHA  V7.2.1) 9.2.1 Split policy This section provides an introduction to PowerHA split and merge policies before PowerHA for  AIX V7.2.1. For more information, see the following IBM Redbooks: Before PowerHA V7.1, when a cluster split occurs, the backup node tries to take over the  resources of the primary node, which results in a split-brain situation. The PowerHA split policy was first introduced in PowerHA V7.1.3 with two options: This is the default option where the primary and backup nodes operate independently of  each other after a split occurs, resulting in the same behavior as earlier versions during a  split-brain situation. This option is applicable to only clusters with sites configured. When a split occurs, the  partition that fails to acquire the Small Computer System Interface (SCSI) reservation on  the tiebreaker disk has its nodes restarted. For a two-node cluster, one node is restarted,  as shown in Figure 9-3 on page 327. 326  IBM PowerHA SystemMirror V7.2.3 for IBM AIX and V7.2.2 for Linux