Shared Memory Communications reference information

SMC Version 2 (SMCv2) defines the specifications that enable multiple IP subnet capability for SMC. The multiple subnet capability is enabled by updates to the underlying networking specifications for RoCE (referred to as RoCEv2) and the IBM Z Internal Shared Memory (ISM) feature (referred to as ISMv2) along with updates to the related technologies. SMCv2 was announced in the IBM z/OS V2R4 3Q2020 new functions and enhancement RFA.

For additional SMC background information, see the original SMC (version 1) information below.

SMC-Dv2 provides SMC-D support when the associated TCP/IP connection spans multiple IP subnets. SMC-Dv2 requires updates to the IBM Z ISM feature introduced on the IBM z15 for Internal Shared Memory (ISM) Version 2 (ISMv2) virtual PCI function. ISMv2 provides support for SMC-Dv2.

The following reference information provides background for the original SMC support and the related solutions.

The IBM zEnterprise® EC12 (and BC12) and z/OS® V2R1 introduce optimized communications with an innovative solution: Shared Memory Communications-Remote Direct Memory Access (RDMA) or SMC-R.

With SMC-R, IBM Z® network capability takes a new leap, strengthening performance for sharing data and reducing data transmission network overhead. The new IBM Z RDMA over Converged Ethernet (RoCE) feature, 10 GbE RoCE Express®, enables industry-standard RDMA capability on the 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. SMC-R provides application transparent exploitation of this new RoCE feature reducing the network overhead and latency of data transfers, effectively offering the benefits of optimized network performance across processors. This breakthrough also lowers the CPU cost associated when moving large amounts of data.

The IBM z13® and z13s® introduces Internal Shared Memory (ISM) virtual PCI function. ISM is a virtual PCI network adapter that enables direct access to shared virtual memory providing a highly optimized network interconnect for IBM Z intra-CPC communications. z/OS V2R2 (PTF) introduces the capability to exploit ISM with Shared Memory Communications-Direct Memory Access or SMC-D. SMC-D provides the next generation of highly optimized intra-CPC communications.

The SMC Applicability Tool (SMC-AT) was created to help you evaluate the applicability and value of SMC-R and SMC-D in your environment with minimal effort and minimal impact. SMC-AT is integrated within the TCP/IP stack (via PTF) and will gather new statistics that are used to project SMC applicability and benefits for the current system. SMC-AT does not require any special hardware.