Red Hat Training

A Red Hat training course is available for Red Hat Enterprise Linux

Chapter 12. Xen Para-virtualized Drivers

Para-virtualized drivers provide increased performance for fully virtualized Red Hat Enterprise Linux guests. Use these drivers if you are using fully virtualized Red Hat Enterprise Linux guests and require better performance.

Note

There are other para-virtualized drivers for Windows for both Xen and KVM hypervisors.
For Windows guests on Xen hosts, see the Red Hat Enterprise Linux 5 Para-virtualized Windows Drivers Guide, which covers installation and administration.
For Windows guests on KVM hosts, see Chapter 13, KVM Para-virtualized Drivers.
The RPM packages for the para-virtualized drivers include the modules for storage and networking para-virtualized drivers for the supported Red Hat Enterprise Linux guest operating systems. These drivers enable high performance throughput of I/O operations in unmodified Red Hat Enterprise Linux guest operating systems on top of a Red Hat Enterprise Linux 5.1 (or greater) host.
The supported guest operating systems are:
  • Red Hat Enterprise Linux 3
  • Red Hat Enterprise Linux 4
  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6

Note

The minimum guest operating system requirements are architecture dependent. Only x86 and x86-64 guests are supported.
The drivers are not supported on Red Hat Enterprise Linux guest operating systems prior to Red Hat Enterprise Linux 3 .
Using Red Hat Enterprise Linux 5 as the virtualization platform allows system administrators to consolidate Linux and Windows workloads onto newer, more powerful hardware with increased power and cooling efficiency. Red Hat Enterprise Linux 4 (as of update 6) and Red Hat Enterprise Linux 5 guest operating systems are aware of the underlying virtualization technology and can interact with it efficiently using specific interfaces and capabilities. This approach can achieve similar throughput and performance characteristics compared to running on the bare metal system.
As para-virtualization requires a modified guest operating system, not all operating systems can use para-virtualization. For operating systems which can not be modified, full virtualization is required. Full virtualization, by default, uses emulated disk, network, video and other hardware devices. Emulated I/O devices can be very slow and are not suited for applications requiring high disk and/or network throughput. The majority of the performance loss with virtualization occurs through the use of emulated devices.
The para-virtualized device drivers are included in the Red Hat Enterprise Linux packages. The drivers bring many of the performance advantages of para-virtualized guest operating systems to unmodified operating systems because only the para-virtualized device driver (but not the rest of the operating system) is aware of the underlying virtualization platform.
After installing the para-virtualized device drivers, a disk device or network card will continue to appear as a normal, physical disk or network card to the operating system. However, now the device driver interacts directly with the virtualization platform (with no emulation) to efficiently deliver disk and network access, allowing the disk and network subsystems to operate at near native speeds even in a virtualized environment, without requiring changes to existing guest operating systems.
The para-virtualized drivers have certain host requirements. 64 bit hosts can run:
  • 32 bit guests.
  • 64 bit guests.
  • a mixture of 32 bit and 64 bit guests.

12.1. System requirements

This section provides the requirements for para-virtualized drivers with Red Hat Enterprise Linux.
Installation

Before you install the para-virtualized drivers the following requirements (listed below) must be met.

Important

All versions of Red Hat Enterprise Linux from 4.7 and 5.3 have the kernel module for the para-virtualized drivers, the pv-on-hvm module, in the default kernel package. That means the para-virtualized drivers are available for Red Hat Enterprise Linux 4.7 and newer or 5.3 and newer guests.

Note

The para-virtualized guest drivers are enabled by default for guests running Red Hat Enterprise Linux 6.1 and newer on Xen hosts. Using the xen_pv_hvm=enable kernel boot parameter is no longer required for these guests.
You will need the following RPM packages for para-virtualized drivers for each guest operating system installation.
Minimum host operating system version:
  • Red Hat Enterprise Linux 5.1 or newer.
Minimum guest operating system version:
  • Red Hat Enterprise Linux 5.1 or newer.
  • Red Hat Enterprise Linux 4 Update 6 or newer.
  • Red Hat Enterprise Linux 3 Update 9 or newer.
Red Hat Enterprise Linux 5 requires:
  • kmod-xenpv.
Red Hat Enterprise Linux 4 requires:
  • kmod-xenpv,
  • modules-init-tools (for versions prior to Red Hat Enterprise Linux 4.6z you require modules-init-tools-3.1-0.pre5.3.4.el4_6.1 or greater), and
  • modversions.
Red Hat Enterprise Linux 3 requires:
  • kmod-xenpv.
You require at least 50MB of free disk space in the /lib file system.