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SMC-R Protocol Strengthens Data Sharing Performance While Reducing CPU Costs


The IBM zEnterprise* EC12 (and BC12) and z/OS* V2.1 introduce optimized communications with an innovative solution: Shared Memory Communications-Remote Direct Memory Access (RDMA) or SMC-R.

With SMC-R, System z* network capability takes a new leap, strengthening performance for sharing data and reducing data transmission network overhead. Mobile and social computing, smarter computing applications and analytics are driving the proliferation of data on the mainframe—creating a need for high-performance communications.

The System z platform has long provided HiperSockets* technology for high-performance LPAR-to-LPAR communication within the same Central Processor Complex (CPC). For CPC-to-CPC communication, however, SMC-R is a new way of reducing the network overhead and latency of data transfers, effectively offering the benefits of HiperSockets across processors. This breakthrough also lowers the CPU cost associated with moving large amounts of data.

The new RDMA over Converged Ethernet (RoCE) feature—10GbE RoCE Express—enables industry-standard RDMA capability on the System z platform. As an RDMA-capable network interface card (RNIC), it can transfer data using direct memory-to-memory communication, reducing the CPU overhead of the networking software stack. An overview of RDMA technology is shown in Figure 1.

Based on an RDMA enabled network fabric, extensions to the InfiniBand-standard RoCE allow existing Ethernet infrastructures to be leveraged to exploit RDMA-based solutions. The System z RoCE Express feature provides such optimized network access.

The Direct or Indirect Approach

Software exploitation options for RDMA generally fall into two categories:

  1. Direct RDMA exploitation using low-level APIs
  2. Indirect exploitation using transparent APIs

Direct exploitation requires significant investment in applications changes and coordination in solutions, and imposes new network administrative requirements. Ideally, what’s needed is an indirect, transparent solution that achieves the performance benefits of RDMA, requires no application changes and preserves the key network qualities of service clients with enterprise data center networks demand.

SMC-R represents a new “sockets over RDMA” protocol IBM created to meet these objectives. It’s intended to become an open, pervasive industry protocol. Accordingly, an informational draft request for comment (RFC) has been submitted to the Internet Engineering Task Force.

Gus Kassimis is a System z networking architect and designer in z/OS CommServer and one of the lead architects of the SMC-R protocol.

Jerry Stevens is a senior technical staff member with IBM Software Group and works in AIM Enterprise Networking Solutions Architecture Strategy and Design with a focus on communications hardware architecture. He has more than 25 years of experience with z/OS network communications.


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