This tip is part of our guide on the different kinds of hypervisors. In this section on Type 1 vs. Type 2 hypervisors, you'll learn how the two approaches work and discover the pros and cons of each.
- Type 1, which is considered a bare-metal hypervisor and runs directly on top of hardware. The Type 1 hypervisor is often referred to as a hardware virtualization engine.
- Type 2, which operates as an application on top of an existing operating system.
A Type 1 hypervisor provides better performance and greater flexibility because it operates as a thin layer designed to expose hardware resources to virtual machines (VMs), reducing the overhead required to run the hypervisor itself.
Because a Type 1 hypervisor runs directly on the hardware, it is a function in and of itself. Servers that run Type 1 hypervisors are often single-purpose servers that offer no other function. They become part of the resource pool and are designed specifically to support the operation of multiple applications within various VMs.
Typically, a Type 1 hypervisor is more efficient than a Type 2 hypervisor, yet in many ways they both provide the same type of functionality because they both run the same kind of VMs. In fact, you can usually move a VM from a host server running a Type 1 hypervisor to one running a Type 2 hypervisor and vice versa. A conversion may be required, but the process works.
Because they run directly on the hardware, Type 1 hypervisors support hardware virtualization. Because they run as an application on top of an operating system, Type 2 hypervisors perform software virtualization.
Understanding virtualization hypervisor usage
By their very nature, Type 1 hypervisors are production hypervisors or hypervisors that run VMs offering services to users. Type 2 hypervisors offer a series of different services, but they're rarely used in production. A general-purpose operating system that is required to run Type 2 hypervisors often performs other services, so it cannot devote 100% of the hardware resources to VMs. Therefore, you need a Type 1 hypervisor to run your production VMs.
Type 1 hypervisors are VM monitors that are designed to keep track of all of the events that occur within a VM and, when required, provide -- or deny -- access to appropriate resources to meet VM operating requirements. Ideally, the VM monitor will perform its operations through the use of policies that contain all of the settings assigned to a particular VM. Consider a hardware virtualization hypervisor when you need to perform any of the following:
- System consolidation: Virtualization hypervisors support the operation of multiple systems on the same physical hardware, reducing costs and the physical server footprint while delivering similar and often improved services.
- System testing: Hypervisors support the isolation of systems, letting you test new software and applications without affecting production. They also provide a low-cost testing alternative to physical systems.
- Heterogeneous system operation: Hypervisors support the simultaneous execution of multiple operating systems on the same physical hardware, letting organizations run heterogeneous systems on reduced hardware footprints.
- Hardware optimization: Hypervisors increase hardware usage through the operation of multiple workloads on each physical host server. Server usage can increase from 5% to 10% to upwards of 60% or 70%.
- Application high availability: By sharing workloads through technologies such as failover clustering, servers running virtualization hypervisors can support application high availability and ensure that services are always available when running inside VMs.
- Resource optimization: By running different applications in separate VMs, hypervisors can increase resource use because each application requires a number of resources at different times.
- Service flexibility: Because hypervisors support the operation of systems through VMs, organizations gain flexibility because VMs are easier to clone and reproduce than physical machines.
- Dynamic resource management: Virtualization hypervisors support manual or automated resource allocation to VM workloads as peak usage occurs. Because of this, hypervisors provide better support for dynamic resource allocation in data centers.
About the experts:
Danielle Ruest and Nelson Ruest are IT experts focused on continuous service availability and infrastructure optimization. They are authors of several books, including Virtualization: A Beginner's Guide and Windows Server 2008, The Complete Reference from McGraw Hill Osborne as well as the MCITP Self-Paced Training Kit (Exam 70-238): Deploying Messaging Solutions with Microsoft Exchange Server 2007 from MS Press. Their latest book is a training kit for Microsoft exam titled 70-652: Configuring Windows Server Virtualization with Hyper-V from MS Press. Contact them at firstname.lastname@example.org.