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KVM provides two emulated PCI IDE interfaces. An emulated IDE driver can be

used to attach any combination of up to four virtualized IDE hard disks or

virtualized IDE CD-ROM drives to each virtual machine. The emulated IDE driver

is also used for virtualized CD-ROM and DVD -ROM drives.

T h e emu lat ed f lo p p y d isk d rive d river

The emulated floppy disk drive driver is used for creating virtualized floppy drives.

4 .3.2. Para-virt ualiz ed devices

Para-virtualization provides a fast and efficient means of communication for guests to use devices

on the host machine. KVM provides para-virtualized devices to virtual machines using the Virtio API

as a layer between the hypervisor and guest.

Some para-virtualized devices decrease I/O latency and increase I/O throughput to near bare-metal

levels, while other para-virtualized devices add functionality to virtual machines that is not otherwise

available. It is recommended to use para-virtualized devices instead of emulated devices for virtual

machines running I/O intensive applications.

All virtio devices have two parts: the host device and the guest driver. Para-virtualized device drivers

allow the guest operating system access to physical devices on the host system.

The para-virtualized device drivers must be installed on the guest operating system. By default, the

para-virtualized device drivers are included in Red Hat Enterprise Linux 4.7 and newer, Red Hat

Enterprise Linux 5.4 and newer and Red Hat Enterprise Linux 6.0 and newer. The para-virtualized

device drivers must be manually installed on Windows guests.

Note

For more information on using the para-virtualized devices and drivers, refer to the Red Hat

Enterprise Linux 6 Virtualization Host Configuration and Guest Installation Guide.

T h e p ara- virt u aliz ed n et wo rk d evice ( virt io - n et )

The para-virtualized network device is a virtual network device that provides network

access to virtual machines with increased I/O performance and lower latency.

T h e p ara- virt u aliz ed b lo ck d evice ( virt io - b lk)

The para-virtualized block device is a high-performance virtual storage device with that

provides storage to virtual machines with increased I/O performance and lower latency. The

para-virtualized block device is supported by the hypervisor and is attached to the virtual

machine (except for floppy disk drives, which must be emulated).

T h e p ara- virt u aliz ed co n t ro ller d evice ( virt io - scsi)

The para-virtualized SCSI controller device is a new feature in Red Hat Enterprise Linux 6.4

that provides a more flexible and scalable alternative to virtio-blk. A virtio-scsi guest is

capable of inheriting the feature set of the target device, and can handle hundreds of

devices compared to virtio-blk, which can only handle 28 devices.

In Red Hat Enterprise Linux 6.4 and above, virtio-scsi is fully supported for the following

guest operating systems:

Red Hat Enterprise Linux 6.4 and above

⁠Chapt er 4 . Int roduct io n t o Red Hat virt ualizat ion product s

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Red Hat ENTERPRISE LINUX 5 - VIRTUALIZATION GUIDE Guida di Installazione Pagina 25