z/VM

Enhanced Definition

z/VM is IBM's virtual machine operating system for the zSystems platform, functioning primarily as a Type 1 hypervisor. It enables the creation and management of multiple virtual machines (VMs), each capable of running its own operating system, such as z/OS, Linux on Z, or z/VSE, on a single physical mainframe or within an LPAR. Its core purpose is to maximize hardware utilization and provide a flexible, isolated environment for diverse workloads.

Key Characteristics

- Type 1 Hypervisor: z/VM runs directly on the mainframe hardware (or within an LPAR) and provides virtualization services to guest operating systems, offering near-native performance and direct access to hardware resources.
- Guest Operating System Support: It can host a wide array of guest operating systems, including multiple instances of z/OS, Linux on Z, z/VSE, and z/TPF, allowing for significant workload consolidation and diverse application environments.
- Control Program (CP): The CP is the hypervisor component that manages physical resources (CPU, memory, I/O) and allocates them to virtual machines, creating the illusion of a dedicated machine for each guest.
- Conversational Monitor System (CMS): CMS is a single-user interactive operating system that runs as a guest under CP, often used for system administration, development, and as a base for other z/VM components and utilities.
- Live Guest Relocation (LGR): z/VM supports Live Guest Relocation, allowing a running virtual machine to be moved from one z/VM system to another without interruption, enhancing availability and flexibility for maintenance or load balancing.
- Resource Management: Provides robust tools for dynamic allocation and management of virtual CPUs, memory, and I/O devices (VSWITCH, VDEV) to optimize resource utilization across guest VMs.

Use Cases

- Server Consolidation: Consolidating multiple physical z/OS images or numerous Linux on Z servers onto fewer physical zSystems, reducing hardware, power, cooling, and administrative costs.
- Development and Test Environments: Providing isolated virtual machines for developers and testers to work on different versions or configurations of z/OS, Linux on Z, or applications without impacting production systems.
- Linux on Z Deployment: Serving as the primary platform for deploying and managing a large number of Linux on Z instances, enabling the mainframe to host open-source, containerized, and cloud-native workloads alongside traditional mainframe applications.
- Disaster Recovery: Facilitating efficient disaster recovery strategies by allowing quick provisioning and activation of backup guest operating systems on a recovery z/VM system, often with fewer physical resources.
- Application Isolation: Running critical applications or different departments' workloads in their own dedicated virtual machines, ensuring resource isolation, security, and preventing interference between diverse environments.

Related Concepts

z/VM operates at a layer above the hardware but below the guest operating systems. It works in conjunction with PR/SM (Processor Resource/System Manager), which provides hardware-level logical partitioning (LPARs). An LPAR can run either z/OS directly or z/VM, which then further virtualizes that LPAR's resources into multiple guest VMs. It is fundamental for hosting Linux on Z distributions, allowing them to leverage the mainframe