Parallel sysplex
One of the most distinguishing features of the z/OS operating system is the way you can cluster z/OS systems in a Parallel Sysplex. Parallel Sysplex, or Sysplex in short, is a feature of z/OS that was built in the 90s that enables extreme scalability and availability. In the previous post we highlighted the z/OS Unix part. Here we will dive into the z/OS Parallel Syplex. A cluster of z/OS instances With Parallel Sysplex you can configure a cluster of z/OS operating system instances. In such a sysplex you can combine the computing power of multiple of z/OS instances on multiple mainframe boxes into a single logical z/OS server. When you run your application on a sysplex, it actually runs on all the instances of the sysplex. If you need more processing power for your applications in a sysplex, you can add CPUs to the instances, but you can also add a new z/OS system to the sysplex. This makes a z/OS infrastructure is extremely scalable. Also, a sysplex isolates your applications from failures of software and hardware components. If a system or component in a Parallel Sysplex fails, the software will signal this. The failed part will be isolated while your application continues processing on the surviving instances in the sysplex. Special sysplex components: the Coupling Facility For a parallel sysplex configuration, a special piece of software is used: a Coupling Facility. This Coupling Facility functions as shared memory and communication vehicle to all the z/OS members forming a sysplex. The z/OS operating system and the middleware can share data in the Coupling Facility. The type of data that is shared are the things that members of a cluster should know about each other since they are action on the same data: status information, lock information about resources that are accessed concurrently by the members, and caching of shared data from databases. A Coupling Facility runs in a dedicated special operating system, in an LPAR of its own, to which even system administrators do not need access. In that sense it is a sort appliance. A sysplex with Coupling Facilities is depicted below. There are multiple Coupling Facilities to avoid a single point of failure. The members in sysplex connect to the Coupling Facilities. I have not included all the required connections in this picture, as that would become a cluttered view. A parallel sysplex Middleware exploits the sysplex functions Middleware components can make use of the sysplex features provided by z/OS, to create clusters of middleware software. Db2 can be clustered into so-called Datasharing Group. In a Datasharing Group you can create a database that can process queries on multiple Db2 for z/OS instances on multiple z/OS systems. Similarly WebSphere MQ can be configured in a Queue Sharing Group, CICS in a CICSPlex, IMS in an IMSPlex and other software like WebSphere Application Server, IDMS, Adabas and other middleware use parallel sysplex functions to build highly available and scalable clusters. This concept is illustrated in Figure 15. Here you…