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Chapter 4. Introduction to Fedora virtualization products

4.1. KVM and virtualization in Fedora
4.2. libvirt and libvirt tools
4.3. Virtualized hardware devices
4.3.1. Virtualized and emulated devices
4.3.2. Para-virtualized devices
4.3.3. Physical host devices
4.3.4. CPU models
4.4. Storage
4.4.1. Storage pools
4.4.2. Storage volumes
This chapter introduces the various virtualization products available in Fedora.

4.1. KVM and virtualization in Fedora

What 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 Fedora kernel. It can run multiple, unmodified Windows and Linux guest operating systems. The KVM hypervisor in Fedora is managed with the libvirt API and tools built for libvirt (such as virt-manager and virsh). Virtual machines are executed and run as multi-threaded Linux processes controlled by these tools.
Overcommitting
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 Fedora Virtualization Deployment and Administration Guide.
Thin provisioning
Thin provisioning allows the allocation of flexible storage and optimizes the available space for every guest. 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.
KSM
Kernel SamePage 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.

Note

For more information on KSM, refer to the Fedora Virtualization Deployment and Administration Guide.
QEMU guest agent
The QEMU guest agent runs on the guest operating system and allows the host machine to issue commands to the guest operating system.

Note

For more information on the QEMU guest agent, refer to the Fedora Virtualization Deployment and Administration Guide.
KVM guest virtual machine compatibility
To verify whether your processor supports the virtualization extensions and for information on enabling the virtualization extensions if they are disabled, refer to the Fedora Virtualization Deployment and Administration Guide.