A node group is a set of nodes whose members may be individual nodes and other node groups. Individual nodes that belong to a node group are member nodes; node groups that belong to a node group are member node groups. Node groups containing only nodes are flat node groups; node groups containing node groups are hierarchical node groups. Any node group can be resolved into a flat version that contains only valid member nodes.
Dependent nodes cannot be part of a node group but SP-attached servers can be part of a node group just like any other standard SP node.
Commands, except those that directly manage the node groups, issued against a node group have the same effect as issuing the commands against the set of nodes that represent the flat version of the node group.
Node groups are stored persistently in the SDR. A node group in the SDR is made up of two components: a name and a definition list. A node group name must start with an alphabetic character (A-Z, a-z), but can then contain a sequence of alphanumeric characters (A-Z, a-z, 0-9), a period (.) or an underbar (_). (Thus named, node groups can be easily differentiated from node objects, whose names are a string of numeric characters representing the node number.) A node group name may not contain spaces. The definition list of a node group is made up of a list of nodes and node groups that belong to the node group directly, (not through member node groups).
Some node groups exist within a system partition (partition-bound node groups or local node groups) and some node groups ignore system partition boundaries (global node groups). Partition-bound or local node groups can be accessed only within the context of the system partition they belong to. Global node groups are not bound to any system partition, but can be acted on only by commands that accept the -G flag or when using the SP Perspectives GUI with a Global view of the SP system. Partition-bound and global refer to the mode of the node group.
Partition-bound node groups (local node groups) are stored in the partitioned SDR class NodeGroup. Global node groups are stored in the system SDR class SysNodeGroup. Valid member nodes of a partition-bound node group must be node numbers that are defined in that particular system partition. Valid member nodes of a global node group are node numbers that are defined in that particular SP system (the union of all nodes in each system partition). Any node number or node group can be added to the definition list of a node group, but only valid member nodes or valid member node groups will be used when resolving (flattening) the node group.
Most SP system end users work within system partitions and, therefore, will use partition-bound node groups.
System Administrators, however, will often find it necessary, and advantageous, to work with global node groups. The use of global node groups allows a System Administrator to perform certain tasks, such as installing a daemon on specific nodes or powering off and reconfiguring all nodes on which a given application is running, without regard to system partitions.
Partition-bound node groups and global node groups are different, but they both function to provide a naming facility for sets of nodes.
When creating a node group or adding to an existing node group's definition list, you can use the command line interface or SMIT panels to add any node number or node group. The member node group does not need to have been defined at the time it is added to another node group's definition list. The member node does not have to be a valid node number for a system partition or even the SP system at the time it is added to another node group's definition list. In this way, you can create node groups to accommodate future growth or changes, such as adding nodes or repartitioning your SP system.
Only users that have the appropriate authority to modify objects in the SDR can create, modify or delete node groups. Any user that has the appropriate authority to read objects from the SDR can reference existing node groups. Any user can modify or reference node groups created by other users, provided they have the appropriate SDR authority. For more information on the authority needed to access the SDR, refer to Authorization.
When a node group is resolved into its flat version, only valid member nodes will appear in the flat version and only valid member node groups will be resolved recursively to produce the flat version. If a node group is a partition-bound node group, when it is flattened all of its member nodes and member node groups must be defined in the same system partition; if they are not, they will not be used to produce the flat version of this node group. If the node group is a global node group, when it is flattened all of its member nodes must be node numbers for the system and member node groups must also be defined as global node groups. Member nodes or member node groups that do not correspond to entities in persistent storage will be ignored when producing a flat version of the node group. A node group's flat version can be empty.
The following is a simple example of how a partition-bound node group will be resolved into a flat list of node numbers.
system partition P1 contains nodes 1, 2, 5, 6, 9, 10, 13, 14 system partition P1 contains node groups A, B, C Node Group A name = A; definition list = 1, 2, B, C, D Node Group B name = B; definition list = 1, 2, 3, 4, 5, 6 Node Group C name = C; definition list = 13, 14 flat(A) = nodes 1, 2, 5, 6, 13, 14 flat(B) = nodes 1, 2, 5, 6 flat(C) = nodes 13, 14
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