Installation guide

Chapter 4. Introduction to Red Hat virtualization products
This chapter introduces the various virtualization products available in Red Hat Enterprise Linux.
4.1. KVM and virt ualizat ion in Red Hat Ent erprise Linux
Wh at is KVM?
KVM (Kernel-based Virtual Machine) is a full virtualization solution for Linux on AMD64 and
Intel 64 hardware that is built into the standard Red Hat Enterprise Linux 6 kernel. It can run
multiple, unmodified Windows and Linux guest operating systems. The KVM hypervisor in
Red Hat Enterprise Linux is managed with the lib virt API and tools built for lib virt (such
as vi rt-manag er and vi rsh). Virtual machines are executed and run as multi-threaded
Linux processes controlled by these tools.
O verco mmit t in g
The KVM hypervisor supports overcommitting of system resources. Overcommitting means
allocating more virtualized CPUs or memory than the available resources on the system.
Memory overcommitting allows hosts to utilize memory and virtual memory to increase guest
densities.
Important
Overcommitting involves possible risks to system stability. For more information on
overcommitting with KVM, and the precautions that should be taken, refer to the Red
Hat Enterprise Linux 6 Virtualization Administration Guide.
T h in p ro visio n in g
Thin provisioning allows the allocation of flexible storage and optimizes the available
space for every guest virtual machine. It gives the appearance that there is more physical
storage on the guest than is actually available. This is not the same as overcommitting as
this only pertains to storage and not CPUs or memory allocations. However, like
overcommitting, the same warning applies.
Important
Thin provisioning involves possible risks to system stability. For more information on
thin provisioning with KVM, and the precautions that should be taken, refer to the
Red Hat Enterprise Linux 6 Virtualization Administration Guide.
KSM
Kernel Same-page Merging (KSM), used by the KVM hypervisor, allows KVM guests to share
identical memory pages. These shared pages are usually common libraries or other
identical, high-use data. KSM allows for greater guest density of identical or similar guest
operating systems by avoiding memory duplication.
Red Hat Ent erprise Linux 6 Virt ualizat io n G et t ing St art ed G uide
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