The following terms used in this document are defined as follows:
backup node - A backup node will take over the role of the primary access point for resources associated with the cluster resource group (CRG) in the event of an outage on the primary node. A backup node contains a copy of the resources that is kept current by replication software. The recovery domain determines the sequence in which the exit program will attempt to activate backup nodes during a switchover or failover. The role of backup node is not supported for peer CRGs.
cluster - A cluster is a collection of interconnected complete computers that work together as a single unified computing resource. The cluster is made up of one or more cluster nodes and is identified by a name comprised of 10 or fewer characters.
cluster resources - Cluster resources are the resources that are required to be highly available by your business and are available to the nodes within a cluster. Cluster resources can be either moved or replicated to one or more nodes within a cluster. Examples include applications, data libraries, devices, and disk units. Resources are identified in cluster resource groups and controlled through cluster resource group exit programs.
cluster resource group (CRG) - A cluster resource group is an IBM i system object that identifies a collection of cluster resources to be monitored and managed as a single unit. Each CRG defines the relationship between the nodes associated with those resources in a recovery domain that determines role of each node in the CRG as well as the degree to which each can participate in events such as synchronizing or performing a recovery action. Several types of CRGs are available. Each of the following CRG types is designed for a specific type of cluster resource: application, data, device, and peer.
CRG exit program - Each CRG has a CRG exit program that is called on each active node in the CRG’s recovery domain in response to a cluster event. The exit program manages cluster events for the environment established by the CRG. All possible cluster events have a pre-determined response in the exit program code.
Broadcast replication - A broadcast replication configuration consists of three or more nodes where a single source node feeds two or more target nodes. For example, in a three-node broadcast replication, system A is the source node to both system B and system C.
Cascade replication - A cascade replication configuration consists of three or more nodes in series. For example, a three node cascade replication starts with system A as the source node for system B. System B is the source node for System C.
Data group set - A data group set is the total number of data groups needed to enable replication between all nodes in a cluster. The first part of the three-part name of each data group in the set is the same. Not all of the data groups in the set will be active at the same time.
Node - A node refers to one of two or more logical system definitions that make up a valid replication instance. For non-LPAR systems, a node represents the entire system footprint. For LPAR systems, a node represents one of the LPAR partitions.
Peer node - A node identified as peer has no order within the recovery domain. The peer role is only supported by peer CRGs. The access point to the resources in the peer CRG is controlled by the cluster management application.
Primary node - This node is the primary access point for the resources associated with a CRG. Only one primary node is allowed. For an application CRG, this is the node where the application is currently running. For a data CRG, this node is the source of data for the resources to be replicated. For a device CRG, this node is the current owner of the devices in the CRG. The role of primary node is not supported for a peer CRG.
Recovery domain - A recovery domain identifies the current role of each node within the CRG. The recovery domain also determines the order in which nodes can become the primary access point in the event of an outage. Each CRG defines its own recovery domain.
Replicate node - A replicate node contains a copy of the resources associated with the CRG, but cannot become the primary node or a backup node as the result of a switchover or failover. Replicate nodes are optional. They are reserved for those systems which are either not powerful enough to host applications, are used for queries and reports only, or are perhaps used as a data warehouse server. For peer CRGs, nodes defined as replicate represent an inactive access point.
Replication instance - A replication instance refers to a group of nodes that make up your replication environment.
Simple replication - A simple replication configuration consists of two nodes, a source node (primary) and a target node (backup).