zHyperLink Express
IBM zHyperLink is a technology that can provide up to a 5x reduction in I/O latency through an enhanced Synchronous I/O model. This goal is achieved by using a direct connection between an IBM Z platform and IBM Storage.
This chapter describes the zHyperLink connectivity option, which was introduced with the z14 and DS888x.
This chapter includes the following topics:
3.1 Description
The zHyperLink technology was created to provide fast access to data through a low latency, short distance, direct connection between the IBM Z platform and IBM Storage. This short-distance, direct connection is intended to speed up DB2 for z/OS blocking read requests.
Working with the FICON SAN Infrastructure, zHyperLink can improve application response time by cutting I/O-sensitive workload response time by up to 50% without requiring application changes.
The zHyperLink Express feature in the z14 (or newer Z platform) allows you to make synchronous I/O requests for data that is in the storage cache of the IBM DS888x. This process is done by directly connecting a zHyperLink Express port in the z14 to an I/O Bay zHyperLink port of the DS888x.
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Note: zHyperLink connections complement FICON channels, they do not replace them. Only z/OS and Extended Count Key Data (ECKD) are supported, and the z/OS image must not run as a guest under z/VM.
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3.2 zHyperLink elements
Synchronous I/O is an I/O model type that is used as part of the zHyperLink technology. It allows the operating system to read data records synchronously, thus avoiding the scheduling and interrupt overhead associated with asynchronous operations.
A new Synchronous I/O command was defined to z/OS to synchronously read one or more data records. In addition, an option is provided to allow z/OS to initiate a Synchronous I/O command and return control to perform other processing requests.
When a traditional I/O operation is requested by a task to start the Input/Output Supervisor (IOS), the I/O operation is not handled by the central processor (CP) assigned to the z/OS LPAR. There are specialized components to do the job: SAPs and channel programs.
An SAP is a special processing unit (PU) that helps set up the I/O operation. It finds an available channel path to the device and ensures that the I/O operation starts. However, an SAP is not responsible for the data movement between the storage control unit and z/OS LPAR memory. It is the channel program that communicates with control unit to manage the data movement. After the I/O operation completes, an I/O interrupt notifies the CP so that IOS can be run again.
For Synchronous I/O, the CP directly issues the I/O request to the storage control unit through a zHyperLink connection with a new z/OS I/O command and new hardware capabilities (zHyperLink Express feature, Z firmware, a DS888x I/O system board). The SAP and channel subsystem are bypassed with the Synchronous I/O model. I/O interrupts and I/O path-lengths are minimized, resulting in improved performance.
3.3 Connectivity
The IBM zHyperLink Express takes up one slot in the PCIe I/O drawer and has two ports. Both ports are on a single PCHID. The zHyperLink Express uses PCIe Gen3 technology, with x16 lanes that are bifurcated into x8 lanes. It is designed to support distances up to 150 meters at a link data rate of 8 GBps.
Figure 3-1 shows a zHyperLink Express feature in the z14 connecting to a zHyperLink feature in the I/O Bay of a DS888x.
Figure 3-1 zHyperLink point-to-point connectivity
The zHyperLink Express (FC 0431) is only available on the z14 and newer Z platforms. It requires z/OS 2.1 or later and 24x MTP-MTP cables to connect to a DS888x.
The zHyperLink Express feature is an IBM-designed PCIe adapter. It uses off-the-shelf industry components, including a PLX PCIe switch with a DMA engine and various PCIe interface components. It is managed by using native z/PCI commands, with enhancements for Synchronous I/O.
Up to 16 zHyperLink Express adapters can be installed in a z14, thus allowing up to 32 links.
The zHyperLink Express feature works as native PCIe adapter that can be shared by multiple LPARs. Each port can support up to 127 Virtual Functions (VFs), with one or more VFs/PFIDs being assigned to each LPAR. This configuration supports a maximum of 254 VFs per adapter.
For the DS888x with firmware R8.3 or above, the I/O Bay system board is updated to support the zHyperLink interface. This process includes the update of the PEX 8732 switch to PEX8733 that includes a DMA engine for the zHyperLink transfers, and also the upgrade from a copper to optical interface by provided a CXP connector.
A 24x MTP-MTP cable is required for each port of the zHyperLink Express feature. It is a single 24-fiber cable with Multi-fiber Termination Push-on (MTP) connectors. Internally, the single cable houses 12 fibers for transmit and 12 fibers for receive. Two fiber type options are available with specifications that support different distances for the zHyperLink Express:
•Up to 150 m: OM4 50/125 micrometer multimode fiber optic cable with a fiber bandwidth wavelength of 4.7 GHz-km @ 850 nm.
•Up to 100 m: OM3 50/125 micrometer multimode fiber optic cable with a fiber bandwidth wavelength of 2.0 GHz-km @ 850 nm.
3.4 References
The following publications contain information that is related to the topics covered in this chapter:
•IBM DS8880 and IBM z Systems® Synergy, REDP-5196
•Enhancing Value to Existing and Future Workloads with IBM z13, REDP-5135
•“Making DB2 Zip with IBM’s Hyperwrite” in IBM Systems Magazine at:
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