The ring

The ring consists of one or more systems connected to each other by communication links. The links are used to pass information about requests for global resources from one system to another in the complex. Requests are made by passing a message or token, called the ring system authority message (RSA-message), between systems in a round-robin or ring fashion. There is one RSA token in a global resource serialization ring complex.

Figure 1. The Conceptual View of the Ring Complex

When a system receives the RSA, it inserts global ENQ and DEQ information, and passes it along to the next system to copy. It also makes a copy of the global ENQ/DEQ information that was inserted by other systems. When the RSA returns to the originating system, it knows that all other systems have seen its request, so the request is removed. The system can now process those requests by adding them to the global resource queues, and can now determine which jobs own resources, and which jobs must wait for resources owned by other jobs. Each system takes this information and updates its own global queues.

For various reasons, such as system or link failure, not all systems in a complex might be actively using global resource serialization. The ring is made up of all systems in a global resource serialization complex that are actively using global resource serialization to serialize access to global resources.

Systems participating in a ring are dependent on each other to perform global resource serialization processing. For this reason, the following areas are all adversely affected as the number of systems in a ring increase.

Storage consumption
Processing capacity
Response time
CPU consumption
Availability and recovery time

Figure 2 shows the basic elements of a four-system global resource serialization ring complex. These elements include the systems, the communication links, and any shared resources (such as DASD) specified by the installation.

Figure 2. Global Resource Serialization Ring Complex

The systems in the complex can use global resource serialization to serialize access to global resources, such as data sets on shared DASD volumes. Global resource serialization in a ring complex uses the links (either XCF paths or the dedicated communication links) to communicate information about global resources from one system in the complex to another.

In a ring sysplex, all the links shown are XCF signalling paths. XCF manages the communication links that global resource serialization uses between systems in a sysplex. XCF can use IBM® Enterprise Systems Connection (ESCON®) channels operating in CTC mode, and list structures in a coupling facility as communication links.
Links between a system in a sysplex and one outside of the sysplex, as well as the links that are between two systems that are both outside of the sysplex, can be parallel CTC adapters dedicated to global resource serialization or an ESCON channel operating in basic mode (ESCON BCTC links). Global resource serialization does not use FICON® (FCTC) or ESCON links that are defined as SCTC.

In this document, “link”, “path”, and “CTC link” can mean a parallel CTC adapter, an ESCON channel operating in basic mode, or if appropriate, a list structure in a coupling facility.

For more information on CTC definitions: