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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 "capped," "uncapped," and "shared" configurations, demonstrating how IBM i is a versatile platform suited for diverse needs.

Logical Partitions (LPARs): Hardware-Level Virtualization

IBM i leverages 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 through LPARs allows you to run multiple operating systems and applications concurrently on the same physical server, optimizing resource utilization and scaling according to needs.

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

Guest Machines: Running Different Operating Systems

IBM i is not limited to running only the IBM i operating system. Through LPARs, you can run different operating systems as guest machines:

• IBM i: Obviously, you can create multiple LPARs that run different instances of IBM i. This is useful for separating development, testing, and production environments.

• Linux: It is possible to run Linux distributions (such as Red Hat Enterprise Linux or SUSE Linux Enterprise Server) as guest machines on LPARs. This offers great flexibility and opens the door to the use of open source software.

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

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

Virtual I/O Server (VIOS): Virtualizing I/O

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 adapters, storage adapters).

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

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

• Flexibility in I/O Allocation: VIOS allows you to allocate I/O resources to different LPARs according to 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 the allocation of CPU and memory resources:

• 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 the configured maximum limit.

  • Predictable Performance: Capped LPARs have more predictable and stable performance and are useful when you want to limit CPU usage to ensure performance for other LPARs.

• Uncapped LPAR:

  • Flexible Resources: An "uncapped" LPAR can use the available CPU in the system up to its configured maximum limit, or even beyond its configured limit if there are unused resources and the job priority is high.

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

• Shared LPAR (Shared Processor Pool):

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

  • Efficient CPU Utilization: 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 LPARs: Are useful for predictable and constant workloads, where you want to guarantee the performance of other LPARs.

• Uncapped LPARs: Are useful for variable workloads, where you want to maximize performance when needed.

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

Virtualization in Action

Virtualization in IBM i allows you to create isolated test environments, run legacy and modern applications concurrently, consolidate servers, and reduce costs. The deep integration with the operating system and support for different operating systems makes IBM i an ideal platform for virtualization.

Conclusions

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

• Consolidation: Allows you to reduce 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 you to optimize the utilization of CPU, memory, and I/O resources.

• Scalability: Allows you to scale according to business needs, adding or removing resources to 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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