HV - Hypervisor
In the IBM mainframe context, a hypervisor is a layer of software or firmware that creates and runs virtual machines (VMs). The primary hypervisor on IBM zSystems is **PR/SM (Processor Resource/Systems Manager)**, which enables a single physical mainframe to be divided into multiple logically independent operating environments, known as Logical Partitions (LPARs). Each LPAR can run its own instance of an operating system like z/OS, z/VM, or Linux on Z.
Key Characteristics
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- Hardware-assisted Virtualization: PR/SM is deeply integrated with the zSystem hardware, leveraging specialized instructions and architectural features for highly efficient and secure virtualization.
- Logical Partitioning (LPARs): It creates isolated LPARs, each with dedicated or shared access to CPU, memory, and I/O resources, providing strong workload separation.
- Resource Management: PR/SM provides sophisticated mechanisms for allocating, sharing, and managing processor, memory, and I/O resources among LPARs, including weight-based dispatching and capping.
- High Isolation and Security: LPARs are highly isolated from each other, preventing failures or security breaches in one LPAR from impacting others, which is crucial for multi-tenant and critical environments.
- Dynamic Resource Changes: Resources (e.g., CPUs, memory) can often be dynamically added to or removed from LPARs without requiring a system reboot, enhancing flexibility and availability.
- Firmware-based: PR/SM is primarily a firmware component of the zSystem hardware, conceptually similar to a "Type-0" or "bare-metal" hypervisor, offering minimal overhead.
Use Cases
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- Workload Consolidation: Running multiple z/OS instances, z/VM, or Linux on Z distributions on a single physical mainframe to reduce hardware footprint, power consumption, and operational costs.
- Environment Isolation: Separating production, development, test, and disaster recovery environments into distinct LPARs to prevent interference and enhance system stability and security.
- Multi-tenancy and Cloud: Hosting multiple independent clients, departments, or cloud instances on a single mainframe, each within its own secure and isolated LPAR.
- Disaster Recovery and High Availability: Creating mirrored LPAR configurations across geographically separated mainframes for robust disaster recovery and continuous operations.
- System Upgrades and Testing: Providing dedicated LPARs for testing new z/OS versions, application upgrades, or system configurations before deployment to production.
Related Concepts
The hypervisor (PR/SM) is foundational to the concept of Logical Partitions (LPARs), as it is the technology that creates and manages these isolated environments. It works in conjunction with z/VM, which itself is a Type-1 hypervisor that runs *within* an LPAR to further virtualize resources and host hundreds or thousands of guest operating systems (e.g., Linux on Z, z/OS development instances). This layered virtualization enables extreme flexibility, resource utilization, and consolidation capabilities on zSystems.
- Strategic Resource Allocation: Carefully plan CPU, memory, and I/O allocations for each LPAR based on workload requirements to ensure optimal performance and prevent resource contention.
- LPAR Weighting and Capping: Effectively utilize PR/SM LPAR weights and capping to prioritize critical workloads and manage resource sharing among LPARs, ensuring service level agreements are met.
- Performance Monitoring: Implement robust monitoring tools (e.g., RMF, SMF) to continuously track LPAR resource utilization, identify potential bottlenecks, and optimize resource distribution.
- Security Configuration: Ensure proper security configurations for LPARs, including access controls, network segmentation, and adherence to security policies, to maintain isolation and protect sensitive data.
- Dynamic Resource Management: Leverage dynamic LPAR capabilities to adjust resources (e.g., add or remove CPUs, memory) on the fly, responding to changing workload demands without service disruption.