Hyper-V Architecture

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Parent and Child Partitions

In Hyper-V one VM is that parent partition while others are child partitions. A partition is a basic unit of isolation supported by the hypervisor. The parent partition, also known as root partition, is the partition that creates and managed child partitions and it has a virtualization stacks to control child partitions. This parent partition owns all resources not owned by the hypervisor and is responsible for Power management, PnP, management of hardware failure events and loading and booting the Hypervisor. In the parent partition, running in kernel mode, there is a Windows Server 2008 guest OS. Within Citrix XenServer, the parent partitioning is called ‘Domain 0’. As mentioned earlier this OS can run as role within Server Core or can be a full installation of Windows Server 2008.

Virtualization Service Provider and Client

Running within the guest OS is the Virtualization Service Provider (VSP) this is a component that runs within the parent partition. This partition owns the hardware. The VSP talks to the device drivers and is offering hardware services to whoever requests them. Running in kernel mode within an ‘Enlightened client’ is the Virtualization Service Client (VSC). This is a client component that runs within a child partition and consumes services. There is one pair of VSP/VSC pair for each device type. Microsoft is providing VSP/VSC pairs for storage, networking, video and input devices for Hyper-V. Third-party Independent Hardware Vendors (IHV) will provide additional VSP/VSC pairs to support additional hardware.

HyperCall Adapter

The Hypercall adapter is a thin layer of software that translates the Citrix XenServer-specific virtualization function calls to Microsoft Hyper-V hypercalls. This results in improved performance for the virtual machine running Linux and better operability when VMs are used in a mixed Hyper-V and Citrix XenServer environment.
VMBus

The Hyper-V architecture also includes a virtual machine bus, or VMbus, for communication between the parent and child partitions, Virtualization Service Providers, and Virtualization Service Clients. On virtualization-optimized processors, these components provide an emulated environment with similar performance characteristics to a dedicated physical computer.

Synthetic and emulated devices:

Synthetic devices are designed to have the lowest overhead for devices. These devices package requests and forward them to a driver in the root over VMBUS which then forwards them to the device after any needed processing. Emulated devices on the other hand emulate a real piece of hardware. Both types of devices are important because to support operating systems that do not have “Integration Components” installed emulated devices drivers are needed. The Synthetic devices are important because they help reduce the CPU overhead when accessing a device. Synthetic device drivers are included in the Integration Components.

Integration Components

Integrations components (ICs) are sets of drivers and services that help your Virtual Machines have more consistent state and perform better by enabling the guest to use synthetic devices. Some ICs that come with Hyper-V are VMBUS (transport for Synthetic devices), Time Sync (used to keep VM clocks in sync with the root partition sometimes called the host), Video Driver, Network Driver and Storage Driver. Windows Server 2008 will come with the integration components pre-installed. For other operating systems, like Windows Server 2003 are Linux you can install ICs.

More Read about Enlightenments and ParaVirtualization here Hyper-V HD • Hyper-V Architecture