System state

The state of the clustered system holds all of the configuration and internal data. The system state information is held in volatile memory.

If the mainline power fails, back up power to a node maintains internal power long enough for the system state information to be stored on the internal disk drive of each node. The write cache data and configuration information that is held in memory is stored on the internal disk drive of the node. If the partner node is still online, it attempts to flush the cache and continues operation with the write cache disabled.

Figure 1 shows an example of a system that contains four nodes. Node 1 is elected as the configuration node. The configuration node can be thought of as the node that controls the updating of system state. If the configuration node fails, the system can elect a new node to take over its responsibilities. When a change is made to the configuration or internal system data, the same change is applied to all nodes. This state-driven model of clustering ensures that all nodes in the system know and maintain the exact system state at any time.

  • A user request is made (1) that results in a change to the system configuration.
  • The configuration node, Node 1, controls the updates to the system state (2).
  • The configuration node then forwards that state change to all nodes, including Node 1. All nodes then make the state change at the same point in time (3).
Figure 1. Clustered system, nodes, and system state
This figure shows a system with a configuration node, nodes, and the system state.
Parent topic: Systems