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Virtualizing Resources on the Mainframe

How to virtually get the most from your System z platform.

How to virtually get the most from your System z platform.

Today's IT networks are being called upon to shoulder ever greater processing demands, leading to the need for the increased use of their server footprints to accommodate these expanding workloads. Virtualization provides a means to abstract the components of today's IT to consolidate, integrate and simplify the network infrastructure and reduce the overall cost of IT network ownership.

Server Virtualization

Server virtualization technology provides a means to configure and deploy multiple logical server configurations on a common physical footprint to provide processing and usage benefits beyond those of the physical configuration. The physical server's resources are abstracted to accommodate the concurrent deployment of multiple "virtual server" instances. Each virtual instance, called a virtual machine (VM) or LPAR, is capable of operating a separate OS instance and its associated software stacks as if each instance was deployed on a separate physical server. This virtual view offers the benefit of not being restricted by the implementation or configuration of the underlying physical server resources. Each virtual instance provides a subset or superset of the various physical server resources that may be dedicated or concurrently shared by multiple VM or LPAR abstractions.

Through server virtualization, the OS "image" operating within a VM or LPAR encapsulation appears to have sole control of a separate physical server and its resources. Such physical resource abstractions can lead to considerable IT consolidation and integration of both server hardware and software and resulting simplification of the IT infrastructure. Virtualization increases the overall use and efficiency of a physical server by managing the servers' otherwise unused physical-resource capacities.

The IBM* System z* platform supports two virtualization implementations:

  • Processor Resource/System Manager (PR/SM) is an LPAR implementation consisting of processor, memory and I/O infrastructure virtualization firmware and associated hardware, which provides up to 60 high-performance LPARs for deployment of high-utilization, business-critical production-class workloads. Each LPAR is assigned a unique, non-shared memory space, one or more processors and associated I/O resources. The assigned processors and I/O resources may be dedicated to specific LPARs, or - more commonly - shared by multiple partitions. The controlling PR/SM LPAR hypervisor dynamically and transparently manages the concurrent use of shared processor and I/O resources with low system-virtualization overheads. LPAR and the associated workload co-location within the physical servers' symmetric multiprocessor (SMP) infrastructure can improve the use of the server's resources as well as provide a single point of management control for their workloads and (typically) shared databases.
  • This level of server virtualization enables System z processor-utilization levels to reach more than 90 percent. PR/SM provides other virtualization capabilities such as high-speed virtual LANs (HiperSockets*) that allow software images to communicate across LPARs at SMP memory speeds not seen on TCP/IP external networks operating at wire speeds. These communications can also occur without additional overheads (e.g., data conversions, data compression/decompression, etc.) like when the communicating software images are deployed on separate physical server platforms.
  • z/VM* is a System z implementation that enables the deployment of multiple VM abstractions with similar processor and I/O-virtualization capabilities as the PR/SM LPAR hypervisor. The z/VM software hypervisor provides virtualization capabilities and resource abstractions beyond PR/SM to accommodate large numbers of lower utilization VM instances and many functions designed to accommodate the concurrent development and testing of new application workloads on a single server footprint.

Additionally, z/VM can virtualize logical instances of server resources that don't physically exist. For example, it can create virtual processor instances and then transparently time-share their execution on a single physical processor, creating the illusion of a multiprocessor server. It can also use a physical resource to simulate a different type of resource. For example, it can simulate an I/O resource (such as a virtual disk) or network (such as a virtual LAN) using server memory. Such memory-based virtualizations can also enhance the overall efficiencies by reducing latencies when compared to the physical resources they represent.

Server memory demands can increase exponentially when servicing strategic programming models such as Java and XML, creating increased virtualization demands on a system's most heavily virtualized resource: program-addressable RAM.

Les Wyman has held numerous technical and technical-leadership positions in programming, channel engineering and mainframe architecture during his IBM career. Les can be reached at lwyman@us.ibm.com.



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Virtualizing Resources on the Mainframe

How to virtually get the most from your System z platform.

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