Chapter 1. General Introduction to Virtualization
1.1. What is Virtualization?
Virtualization is a broad computing term used for running software, usually multiple operating systems, concurrently and in isolation from other programs on a single system. Virtualization is accomplished by using a hypervisor. This is a software layer or subsystem that controls hardware and enables running multiple operating systems, called virtual machines (VMs) or guests, on a single (usually physical) machine. This machine with its operating system is called a host. For more information, see the Red Hat Customer Portal.
There are several virtualization methods:
- Full virtualization
- Full virtualization uses an unmodified version of the guest operating system. The guest addresses the host’s CPU via a channel created by the hypervisor. Because the guest communicates directly with the CPU, this is the fastest virtualization method.
- Paravirtualization uses a modified guest operating system. The guest communicates with the hypervisor. The hypervisor passes the unmodified calls from the guest to the CPU and other interfaces, both real and virtual. Because the calls are routed through the hypervisor, this method is slower than full virtualization.
- Software virtualization (or emulation)
- Software virtualization uses binary translation and other emulation techniques to run unmodified operating systems. The hypervisor translates the guest calls to a format that can be used by the host system. Because all calls are translated, this method is slower than virtualization. Note that Red Hat does not support software virtualization on Red Hat Enterprise Linux.
- While KVM virtualization creates a separate instance of OS kernel, operating-system-level virtualization, also known as containerization, operates on top of an existing OS kernel and creates isolated instances of the host OS, known as containers. For more information on containers, see the Red Hat Customer Portal.Containers do not have the versatility of KVM virtualization, but are more lightweight and flexible to handle. For a more detailed comparison, see the Introduction to Linux Containers.To use containers on Red Hat Enterprise Linux, install the docker packages from the Extras channel. Note that Red Hat also offers optimized solutions for using containers, such as Red Hat Enterprise Linux Atomic Host and Red Hat OpenShift Container Platform. For details on container support, see the Red Hat KnowledgeBase.