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Mainframe Storage Networks Reflect Ongoing Modernization

Joseph Gulla discusses IBM Z storage networks and coupling connectivity.

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Last week, I continued this series on the development and rapid change in systems, networks and applications. My focus was networking and I included a detailed discussion of capabilities that you might not have thought much about previously. I concentrated on internal and external LAN connectivity including HiperSockets, the open systems adapter, internal shared memory,  remote direct memory access over converged ethernet and shared memory communication over RDMA. I am sure that one or more of these connection features were new to you as they were for me. This week, I’ll finish this part on networking by discussing IBM Z storage networks and coupling connectivity.

Focus on Storage Networks

Storage networks are concentrated on connecting storage devices containing programs and data with servers that run applications. Let’s take a look at three technologies, FICON, Fibre Channel Protocol (FCP) channels and zHyperLink technologies, to understand how these capabilities support systems and applications use of storage.
The term “Fibre connection” represents the architecture as defined by the InterNational Committee for Information Technology Standards and published as ANSI standards. FICON architecture is an integrated set of rules consisting of five layers (FC-0 through FC-4) for serial data transfer between computers, devices and peripherals.
FICON also represents the names of the various IBM Z server I/O features including the basic FC, FICON, high performance FICON for IBM Z (zHPF) and IBM Z FICON support, benefits, operating modes and topologies. One outstanding feature of FC is that it allows many existing, well-known, and long-implemented channel and networking protocols to run over the same physical interface and media. Accordingly, there is a rich set of standards and terminology associated with its architecture. FICON uses the Single-Byte Command Code Sets, implementation levels SB-3 and SB-4, within the FC standard.
FICON is so important because it provides resilient, high-performance channels for critical workloads by supplying connection to count-key-data and extended count key data devices over FC links.
FCP channels are another important technology that work with storage area networks (SANs), which are specialized networks dedicated to the transport of mass storage data. SANs are typically used to connect large servers in enterprise environments with storage systems and tape libraries. These specialized networks provide reliable and fast data paths between the servers and their storage devices.  
The most common SAN technology used today is the FCP. Within this technology, the traditional SCSI protocol is used to address and transfer raw data blocks between the servers and the storage devices. This is in contrast to other storage communication protocols like the common internet file system or the network file system that operate on file level.
Using FCP and its supporting technologies, there’s an opportunity to consolidate UNIX server farms. This consolidation takes place by attaching to industry-standard SCSI storage controllers and devices with high-performance, virtualized connections for z/VM, z/VSE, and Linux on Z workloads.
zHyperLink technology, a mainframe attach link, is another important storage technology. zHyperLink is the result of collaboration between Db2 for z/OS, the z/OS OS, IBM Z processors and DS8880 storage that delivers extreme low latency I/O access for Db2 for z/OS Applications. What is the expected value of low latency I/O for DB2 on z/OS Applications? The use of zHyperLinks results in these benefits:
  • Accelerates transaction processing on the mainframe
  • Reduces batch elapsed times by providing faster index splits for Db2 for z/OS (index split performance is the main bottleneck for high volume INSERTs)
  • Decreases additional application development costs needed to meet scalability requirements
  • Avoids additional hardware costs and data sharing instances to meet scalability requirements
  • Enhances system resilience through better handling of unpredictable workload spikes and hardware failures
Do zHyperLinks replace FICON? No, zHyperLink technology complements FICON to accelerate I/O requests that are typically used for transaction processing. These links are point-to-point connections between the central electronic complex and the storage system and are limited to 150-meter distances.
Utilize zHyperLink to help accelerate z/OS Db2 database transactions and leverage short distance, point-to-point PCI-e links with this low-latency connectivity to FICON storage systems.

Focus on Coupling Connectivity

Coupling connectivity relates to how up to 32 IBM z/OS images, connected to one or more coupling facilities (CFs) use high-speed specialized links for communication and time keeping. The CFs, which are at the heart of the cluster, enable high-speed record-level read/write data sharing among the images in a cluster. Coupling links support communication between z/OS and CFs. What are the main features?
The CF provides critical locking/serialization, data consistency, messaging and queuing capabilities that allow the systems in the sysplex to coordinate and share data. A well-configured cluster has no single point of failure and can provide end users with near continuous application availability over planned and unplanned outages. Coupling characteristics include:
1. Internal coupling supporting high-speed, efficient communication between a CF partition and one or more z/OS logical partitions that are running on the same central processing complex
2. Short distance coupling that connect CFs within 150 meters of distance, using standard PCI-e interfaces for high-speed differential communication
3. Long distance coupling that pushes distances up to 10km with unrepeated RoCE technology and up to 100km driven by IBM Z qualified Dense Wavelength Multiplexers.
IBM's parallel sysplex clustering technology, which relies on coupling connectivity described above, continues to evolve to provide increased configuration flexibility, improved performance and value.

Next Post

Next post, I’ll continue with this series and shift my focus from networks to applications.
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