D.1 Overview D.2 Shared Memory Communication over RDMA D.2.1 RDMA technology overview 476  IBM z14 (3906) Technical Guide As the volume of data that is generated and transmitted by technologies that are driven by  cloud, mobile, analytics, and social computing applications grows, pressure increases on  business IT organizations to provide fast access to that data across the web, application, and  database tiers that comprise most enterprise workloads. SMCs helps to access data faster  and with less latency. They also reduce CPU resource consumption over traditional TCP/IP  for communications. IBM z14 delivers two new RoCE features: 25GbE RoCE Express2 (FC 0430) and 10GbE  RoCE Express2 (FC 0412). The 10GbE RoCE Express (FC 0411) feature can be carried  forward to z14 (from z13/zEC12). SMC-R (RoCE) includes the following features: RDMA over Converged Ethernet (RoCE) is part of the InfiniBand Architecture Specification  that provides InfiniBand transport over Ethernet fabrics. It encapsulates InfiniBand transport  headers into Ethernet frames by using an IEEE-assigned Ethertype. One of the key  InfiniBand transport mechanisms is RDMA, which is designed to allow the transfer of data to  or from memory on a remote system with low latency, high throughput, and low CPU  utilization. Traditional Ethernet transports, such as TCP/IP, typically use software-based mechanisms for  error detection and recovery. They also are based on the underlying Ethernet fabric that uses  a “best-effort” policy. With the traditional policy, the switches typically discard packets that are  in congestion and rely on the upper-level transport for packet retransmission.  However, RoCE uses hardware-based error detection and recovery mechanisms that are  defined by the InfiniBand specification. A RoCE transport performs best when the underlying  Ethernet fabric provides a lossless capability, where packets are not routinely dropped.  GLYPH<SM590000> Remote Direct Memory Access (RDMA) technology provides low latency, high bandwidth,  high throughput, and low processor utilization attachment between hosts. GLYPH<SM590000> SMC-R is a protocol that allows TCP applications to benefit transparently from RDMA for  transferring data. Consider the following points: – SMC-R uses RoCE Express/Express2 adapter as the physical transport layer. – Initial deployment is limited to z/OS to z/OS communications with a goal to expand  usage to more operating systems, and possibly appliances and accelerators. GLYPH<SM590000> Single Root I/O Virtualization (SR-IOV) technology provides the capability to share the  RoCE ExpressExpress2 adapter between logical partitions (LPARs). Consider the  following points: – RoCE Express2 supports 63 Virtual Functions (VFs) per physical port for a total of 126  VFs per PCHID. – RoCE Express supports 31 VFs per PCHID.  GLYPH<SM590000> The maximum number of RoCE Express and RoCE Express2 features that is supported  per z14 is eight (combined).