Cluster architectures and S/390 Parallel Sysplex scalability

Supporting high transaction rates and high availability for on-line transaction processing and emerging applications requires systems consisting of multiple computing nodes. We outline various cluster architectures and describe the factors that motivate the S/390® Parallel Sysplex™ architecture and its resulting advantages. We quantify the scalability of the S/390 Parallel Sysplex and show that the transaction rate supported is close to linear as nodes are added to the system. The key facet of the S/390 Parallel Sysplex architecture is the coupling facility. The coupling facility provides for very efficient intertransaction concurrency control, buffer cache coherency control, and shared buffer management, among other functions, that lead to the excellent scalability achieved. It also provides for effective dynamic load balancing, high data buffer hit ratios, and load balancing after a failure.