As stated earlier, a global resource serialization ring complex consists of one or more systems connected by communication links. Global resource serialization uses the links to pass information about requests for global resources from one system in the complex to another.

Regardless of the physical configuration of systems and links, the global resource serialization complex consists of every system that indicates at IPL time that it is to be part of the complex. For various reasons, such as a system or link failure, not all of the systems in the complex might be actively using global resource serialization at any particular time. Those systems that are actively using global resource serialization to serialize access to global resources make up the global resource serialization ring.

Figure 1 shows a four-system global resource serialization ring complex. When all four systems in the complex are actively using global resource serialization, the complex and the ring are the same.

Figure 1. Fully-Connected Four-System Complex

The complex shown in Figure 1 has a communication link between each system and every other system; such a complex is a fully-connected complex. A sysplex requires full connectivity between systems. Therefore, when the sysplex and the complex are the same, the complex has full connectivity. Although a mixed complex might not be fully connected, a fully-connected complex allows the systems to build the ring in any order and allows any system to withdraw from the ring without affecting the other systems. It also offers more options for recovery if a failure disrupts ring processing.

For example, if system SYS1 in Figure 1 were to fail and end its active participation in serializing access to global resources, it would still be part of the complex, but it would not be part of the ring. Figure 2 shows the ring that would continue processing after system SYS1 stopped serializing access to global resources.

Figure 2. Three-System Ring — SYS1 Failed

Designing a ring complex describes how to design the complex in detail. Operating the ring complex describes how to plan operational procedures for the complex you design.

The concept of the global resource serialization ring is important because, regardless of the physical configuration of systems and links that make up the complex, global resource serialization uses a ring processing protocol to communicate information from one system to another. Once the ring is active, the primary means of communication is the ring system authority message (RSA-message).