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System z Innovations Automatically Define Configurations for Greater Availability


Data centers run a range of business workloads, including batch and transaction processing, business applications, complex data analysis, collaboration and social business. It’s easy to gravitate toward one particular server as being good for all of these workloads; however, they all have different requirements. For that reason, IBM offers different types of servers.

System z* Discovery and Auto-Configuration (zDAC) is the mainframe’s capability to exploit and support incremental additions to a running system in a plug-and-play fashion. The history of how z/OS* and System z evolved into this capability starts with two configuration definition paradigms.

Most distributed servers use a host-discovery methodology to define I/O configurations. OS servers discover devices they’re allowed to use over individual host bus adapters and put them into I/O configurations. Systems administrators use storage-area network (SAN)-based tools to control which servers and host bus adapters are allowed to see which devices. Fabric zoning and logic unit number (LUN) masking are typical techniques for controlling which servers have access to which devices over what paths. When new devices are added to the SAN, distributed servers dynamically discover new resources and put them to use.

System z mainframes, however, use a host-based I/O definition methodology using the Hardware Configuration Dialog (HCD). Devices and channels used to access them are defined by configuration data contained in host processors. The tooling assigns device names, allocates bandwidth by allotting sets of channels used to access devices, and enforces security policy by controlling which LPARs (OS images) can access devices. These host-based tools provide interactive consistency checking between software and processor views of I/O configurations while policing software and hardware limits.

Host configuration definitions are easily modified by defining new configurations and dynamically selecting them. The OS determines the differences between old and new configurations and modifies the I/O configuration to match the new definition.

To simplify the process, z/OS clients desired a plug-and-play capability for adding devices to I/O configurations. Discovery of new devices and their channel attachments eliminates mismatches between planned host definitions and cable plugins. If definitions and actual configurations don’t match, problems are discovered when activating the new configurations and trying to format the new devices and bring them online.

Enterprise class I/O configurations are designed for high availability, so single points of failure and repair must be avoided for critical devices, but planning an I/O configuration to prevent them is a complex activity. Such single points of failure include channel, switch port and control unit port boundaries. A plug-and-play approach can automatically define high-availability configurations, eliminate human error and improve system availability.

Harry M. Yudenfriend is an IBM Fellow with Systems and Technology Group, System z and Power who joined IBM in 1980. He was named an IBM Master Inventor in 2001 and has achieved his 33rd invention plateau.



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