Installation guide

Chapter 2. What is virtualization and migration?
This chapter discusses terms related to virtualization and migration.
2.1. What is virt ualizat ion?
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. Most existing
implementations of virtualization use a hypervisor, a software layer or subsystem that controls
hardware and provides guest operating systems with access to underlying hardware. The hypervisor
allows multiple operating systems, called guests, to run on the same physical system by offering
virtualized hardware to the guest operating system. There are various methods for virtualizing
operating systems:
Fu ll virt u aliz at io n
Full virtualization uses the hardware features of the processor to provide guests with total
abstraction of the underlying physical system. This creates a new virtual system, called a
virtual machine, that allows guest operating systems to run without modifications. The guest
operating system and any applications on the guest virtual machine are unaware of their
virtualized environment and run normally. Hardware-assisted virtualization is the technique
used for full virtualization with KVM (Kernel-based Virtual Machine) in Red Hat Enterprise
Linux.
Para- virt u aliz at io n
Para-virtualization employs a collection of software and data structures that are presented
to the virtualized guest, requiring software modifications in the guest to use the para-
virtualized environment. Para-virtualization can encompass the entire kernel, as is the case
for Xen para-virtualized guests, or drivers that virtualize I/O devices.
So f t ware virt u aliz at io n ( o r emu lat io n )
Software virtualization uses slower binary translation and other emulation techniques to
run unmodified operating systems. Software virtualization is unsupported by Red Hat
Enterprise Linux.
Note
For more information and detailed instructions on guest installation, refer to the Red Hat
Enterprise Linux 6 Virtualization Host Configuration and Guest Installation Guide.
2.2. Migrat ion
Migration describes the process of moving a guest virtual machine from one host to another. This is
possible because the virtual machines are running in a virtualized environment instead of directly on
the hardware. There are two ways to migrate a virtual machine: live and offline.
Mig rat io n T yp es
O f f lin e mig rat io n
⁠Chapt er 2 . What is virt ualiz at ion and migrat ion?
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