Product SiteDocumentation Site

2.2. Red Hat Virtualization Hypervisor

A Red Hat Enterprise Virtualization environment has one or more hosts attached to it. A host is a server that provides the physical hardware that virtual machines make use of. Red Hat Enterprise Virtualization Hypervisor hosts run an optimized operating system installed using a special, customized installation media specifically for creating virtualization hosts. Red Hat Enterprise Linux hosts are servers running a standard Red Hat Enterprise Linux operating system that has been customized after installation to permit use as a host. Both methods of host installation result in hosts that interact with the rest of the virtualized environment in the same way, and so, will both referred to as hosts.
Host Architecture
Figure 2.2. Host Architecture

Kernel-based Virtual Machine (KVM)
The Kernel-based Virtual Machine (KVM) is a loadable kernel module that provides full virtualization through the use of the Intel VT or AMD-V hardware extensions. Though KVM itself runs in kernel space, the guests running upon it run as individual QEMU processes in user space. KVM allows a host to make its physical hardware available to virtual machines.
QEMU
QEMU is a multi-platform emulator used to provide full system emulation. QEMU emulates a full system, for example a PC, including one or more processors and peripherals. QEMU can be used to launch different operating systems or to debug system code. QEMU, working in conjunction with KVM and a processor with appropriate virtualization extensions, provides full hardware assisted virtualization.
For information on the other devices available to guests by QEMU see Appendix C, Virtualized Hardware.
Red Hat Enterprise Virtualization Manager Host Agent, VDSM
In Red Hat Enterprise Virtualization, VDSM performs actions on virtual machines, storage. It also facilitates inter-host communication. VDSM monitors virtualized hosts' resources such as memory, storage, and networking. Additionally, VDSM manages host administration tasks such as virtual machine creation, statistics accumulation, and log collection. A VDSM instance runs on each host and receives management operation information from the Red Hat Enterprise Virtualization Manager. The Red Hat Enterprise Virtualization Manager uses VDSM to manage host administration tasks such as virtual machine creation, statistics accumulation, and log collection.
The Red Hat Enterprise Virtualization Manager uses VDSM as the host management module and establishes communication with it over the re-configurable port 54321.
VDSM-REG
VDSM uses VDSM-REG to register each host with the Red Hat Enterprise Virtualization Manager. VDSM-REG supplies information about itself and its host using port 80 or port 443.
libvirt
Libvirt facilitates the management of virtual machines and the infrastructure that supports them. When Red Hat Enterprise Virtualization Manager is used to initiate virtual machine life-cycle commands (start, stop, reboot), VDSM invokes libvirt on the relevant host machines to execute these host life-cycle commands.
Storage Pool Manager, SPM
The Storage Pool Manager (SPM) is a role assigned to one host in a data center, which gives the SPM host sole authority to make all storage domain structure metadata changes for the data center. This includes creation, deletion, and manipulation of virtual disk images, snapshots, and templates. It also includes allocation of storage for sparse block devices on a Storage Area Network(SAN). The role of SPM can be migrated to any host in a data center. As a result, all hosts in a data center must have access to all the storage domains defined in the data center.
Red Hat Enterprise Virtualization Manager ensures that the SPM is always available. In case of storage connectivity errors, the Manager re-assigns the SPM role to another host.
See Section 3.2, “Role: The Storage Pool Manager” for more information on the Storage Pool Manager.
Guest Operating System
Guest operating systems can be installed in a Red Hat Enterprise Virtualization environment without modification. The guest operating system, and any applications on the guest, are not aware of the virtualized environment and run normally. However, device drivers that allow faster and more efficient access to virtualized devices are available and can be installed inside the guest. You can also install the Red Hat Enterprise Virtualization Agent on guests, which provides enhanced guest information to the management console.