IBM Champions

Introduction
Virtualization has become an essential component of modern IT infrastructure, and IBM i (formerly known as AS/400) stands out for its ability to offer powerful and highly integrated virtualization. In this article, we will explore how IBM i manages virtualization through Logical Partitions (LPARs), guest machines, Virtual I/O Server (VIOS), and the "capped," "uncapped," and "shared" configurations, demonstrating how IBM i is a versatile platform suitable for diverse needs.

Logical Partitions (LPAR): Hardware-Level Virtualization
IBM i utilizes LPAR (Logical Partition) technology to create logical partitions within a single physical server. Each LPAR behaves like a separate server, with dedicated or shared CPU, memory, and I/O resources.

• Isolation and Security: Each LPAR is isolated from the others, ensuring security and preventing interference between different workloads.

• Flexibility and Scalability: Virtualization via LPAR allows running multiple operating systems and applications simultaneously on the same physical server, optimizing resource utilization and scaling based on needs.

• Centralized Management: LPAR management can be centralized, facilitating system administration and resource distribution.

Guest Machines: Running Different Operating Systems
IBM i is not limited to running only the IBM i operating system. Through LPARs, it is possible to run different operating systems as guest machines:

• IBM i: Obviously, multiple LPARs running different instances of IBM i can be created. This is useful for separating development, test, and production environments.

• Linux: Linux distributions (such as Red Hat Enterprise Linux or SUSE Linux Enterprise Server) can be run as guest machines on LPARs. This offers great flexibility and opens the door to using open-source software.

• AIX: Although less common, it is possible to run AIX (IBM's Unix operating system) as a guest machine.

This capability to run different operating systems on the same hardware makes IBM i a versatile platform for diverse business needs.

Virtual I/O Server (VIOS): I/O Virtualization
The Virtual I/O Server (VIOS) is a key component in IBM i virtualization. VIOS is a special virtual machine that manages access to physical I/O resources (e.g., disks, network cards, storage adapters).

• I/O Resource Sharing: VIOS allows multiple LPARs to share physical I/O resources, optimizing hardware utilization.

• Centralized I/O Management: I/O management is centralized in the VIOS, facilitating system administration.

• Flexibility in I/O Allocation: VIOS allows allocating I/O resources to different LPARs based on their needs, ensuring optimal performance.

• Adapter Virtualization: VIOS enables the virtualization of physical adapters, allowing the creation of virtual adapters for different LPARs.

LPAR Configurations: Capped, Uncapped, and Shared
LPARs can be configured in different ways to manage CPU and memory resource allocation:

• Capped LPAR:

  • Limited Resources: A "capped" LPAR has a maximum limit of CPU resources it can use. Even if the physical system has available resources, the capped LPAR cannot exceed its configured maximum limit.

  • Predictable Performance: The capped LPAR has more predictable and stable performance, and is useful when you want to limit CPU usage to guarantee performance for other LPARs.

• Uncapped LPAR:

  • Flexible Resources: An "uncapped" LPAR can use available CPU in the system up to its configured processing capacity entitlement, or even beyond this limit if there are unused resources and the workload's priority allows it.

  • Dynamic Performance: Uncapped LPARs dynamically adapt to the workload, offering superior performance when needed.

• Shared LPAR (Shared Processor Pool):

  • Shared Processor Pool: "Shared" LPARs utilize a "pool" of shared processors. Multiple LPARs can dynamically access processors in the pool, optimizing CPU utilization.

  • CPU Utilization Efficiency: The shared processor pool is ideal for environments with variable workloads, maximizing resource utilization and reducing the risk of underutilization.

Optimal Configuration
The choice between "capped," "uncapped," and "shared" LPARs depends on the specific needs of each environment. In general:

• Capped LPAR: Useful for predictable and constant workloads, where you want to guarantee the performance of other LPARs.

• Uncapped LPAR: Useful for variable workloads, where you want to maximize performance when necessary.

• Shared LPAR: Useful when you want to optimize costs and maximize resource utilization in environments with multiple LPARs.

Virtualization in Action
Virtualization in IBM i allows creating isolated test environments, running legacy and modern applications simultaneously, consolidating servers, and reducing costs. The deep integration with the operating system and support for different operating systems make IBM i an ideal platform for virtualization.

Conclusions
Virtualization in IBM i is a powerful, versatile, and mature solution that offers:

• Consolidation: Allows reducing the number of physical servers, resulting in cost and space savings.

• Flexibility: Offers the flexibility to run different operating systems and applications on the same hardware.

• Resource Optimization: Allows optimizing the use of CPU, memory, and I/O resources.

• Scalability: Allows scaling based on business needs by adding or removing resources from LPARs.

• Security: Offers a secure environment with isolation between LPARs.

If you are looking for a reliable, high-performing, and flexible virtualization platform, IBM i is a solution to consider carefully.

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