Today we released a set of para-virtualized (PV) drivers for use with fully-virtualized (FV) Red Hat Enterprise Linux guests running on a Red Hat Enterprise Linux 5.1 (or later) host.

Red Hat Enterprise Linux 5 introduced native virtualization support when it was released in March 2007. This provided PV guest support for Enterprise Linux 5 guests, offering one of the lowest possible virtualization overheads for applications. PV guest support was subsequently extended to Red Hat Enterprise Linux 4 guests with the 4.5 minor release. Additionally, support for FV guests, which offers the ability to run the same kernel as a non-virtualized system, albeit at lower performance, was also provided.

In performance tests it was clear that PV guests running CPU-centric workloads have less than 5 percent virtualization overhead, while even the most demanding I/O intensive tasks, such as webserving and high performance database I/O loads, perform within 85 percent of bare-metal performance.

With the new PV drivers that we are releasing today, Red Hat extends this caliber of performance to FV guests. The PV drivers released today are virtualization-aware network and disk-drivers used by an FV guest instance of Red Hat Enterprise Linux 3U9, 4.6, 5.1 or later running on a x86-64 or x86 Red Hat Enterprise Linux 5.1 or later host.

All users running FV instances of Red Hat Enterprise Linux 3.9, 4.6 or 5.1 as guests on Red Hat Enterprise 5.1 and later hosts are advised to install these new drivers because they improve I/O performance significantly. The greatest beneficiary of the PV drivers will be customers with Enterprise Linux 3-based workloads, who now can use Red Hat Enterprise Linux 5 Virtualization as a hardware abstraction layer with very low overhead, and so gain access to new hardware that is not supported natively by Enterprise Linux 3.

Additionally, using the new PV drivers with FV guests provides:

  • Increased scalability by raising the limits for attached storage devices and network interfaces.
  • The ability to consolidate on to 64bit Red Hat Enterprise Linux 5 Hosts/Hypervisors and mixing of 32bit and 64bit guests on a single host architecture. While retaining close to bare metal performance.
  • FV guests with PV drivers can be controlled using the included graphical management tools.

Red Hat has released the following performance results for both Intel and AMD-based x86 systems with Enterprise Linux 5.1 / 5.2:

  • Red Hat Enterprise Linux 5.1 on Intel – shows up to 89 percent efficiencies for CPU-intensive loads, SPECint/fp2006, linpack and SPECjbb: and
  • Red Hat Enterprise Linux 5.1 on AMD – as you can see in the table below, scaling up an application in an SMP guest is not completely linear but with 5.1 PV+ AMD’s Rapid Virtualization Indexing (RVI, previously called Nested Pages) virtualization efficiencies improve dramatically. The tables show the results achieved, measured in transactions per minute, with AMD-based 8-cpu and 16-cpu HP systems. Note the dramatic gain provided by RVI combined with PV drivers on a 16-way system.


  • Using the PV drivers in FV guests not only will dramatically improve I/O performance but also significantly improve networking performance
  • A FV guest without PV drivers will not be able to sustain more than 100Mb/s regardless of the underlying physical network card (ie 1GbE)
  • After installing the PV drivers in a FV guest it will be possible to generate networking throughput equal to the capabilities of the underlying physical NIC
  • The chart below shows the significant improvements in networking performance when using the PV drivers for FV guests


  • Additional information can be found in this Red Hat Magazine article
  • Even more performance information can be found by watching our webinar

The drivers are available immediately to existing subscribers of Red Hat Enterprise Linux via the Red Hat Network (RHN) channels of their respective version of Enterprise Linux.

For full documentation regarding installation, configuration and trouble-shooting of these PV drivers, see the Para-Virtualized Drivers for Red Hat Enterprise Linux manual here.

A PDF version of this manual is also available here.