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Virtualization solutions enable you
to run multiple
VMs (virtual machines) on one physical computer. System
virtualization is a technology often used to consolidate systems,
workloads and
operating environments by using a single physical system to
create multiple virtual systems. Current market leaders
include VMWare for Windows and Linux, Microsoft Virtual Server, and the
open
source Xen hypervisor.
At the heart of of system
virtualization is another technology called a Virtual Machine
Monitor (VMM). The VMM provides the underpinnings for
virtualization management, which includes policy-based automation,
virtual hard disk, life cycle management, live migration and
real-time resource allocation.
You can basically think of the VMM as
the part of the code in
firmware
that manages either multiple operating systems or multiple instances
of the same operating system on a single computer system. Its job is
to manage the system's processor, memory and other resources to
allocate what each operating system requires. VMMs provide the
means, through emulation, to divide a single, physical server or
blade, allowing multiple operating systems to run securely on the
same CPU and
increase the CPU utilization.
What the industry has seen lacking
was support for virtualization at the hardware level to
boost the performance of the VMM. This is because the x86 processor architecture did not
previously meet virtualization standards, making virtualization on
the x86
platforms difficult. Starting in 2005 both AMD and Intel made
changes to their x86 architectures and
added virtualization-friendly extensions.
Intel Virtualization
Technology (VT) Xeon
Intel Virtualization Technology (Intel VT) is a set of hardware
enhancements to Intel server and client platforms that provide
software-based virtualization solutions. Intel VT allows a
platform to run multiple operating systems and applications in
independent partitions, allowing one computer system to
function as multiple virtual systems.
AMD-Virtualization (AMD-V)
Opteron
AMD's Virtualization (AMD-V) technology, which takes some tasks
that virtual machine managers (VMMs) perform in software,
through emulation, and simplifies them through enhancements to
the AMD Athlon 64 and Opteron instruction set. AMD
Virtualization Technology was announced in 2004, under the
code-name Pacifica, and AMD released technical details in
mid-2005.
Benefits of Hardware-Assisted Virtualization
Hardware-assisted virtualization changes the
access to the operating system itself. x86 operating systems are
designed to have direct access to system resources to run. With software
virtualization the VMM emulates the required hardware to the operating
system. With hardware-assisted virtualization the operating system has
direct access to resources without any emulation or OS modification. |
Key Terms To
Understanding Virtualization:
virtual machine
A self-contained operating environment that behaves as if it is
a separate computer.
virtualization
In computing, virtualization means to create a virtual version
of a device or resource, such as a server, storage device, network
or even an operating system where the framework divides the resource
into one or more execution environments.
AMD Virtualization
AMD's Virtualization (AMD-V) technology, which takes some tasks
that virtual machine managers (VMMs) perform in software, through
emulation, and simplifies them through enhancements to the AMD
Athlon 64 and Opteron instruction set.
Intel VT
Intel Virtualization Technology (Intel VT) is a set of hardware
enhancements to Intel server and client platforms that provide
software-based virtualization solutions.
emulation
Refers to the ability of a program or device to imitate another
program or device.
x86
Microprocessors made by Intel Corporation form the foundation of all
PCs. The common architecture behind all Intel microprocessors is
known as the x86 architecture. |
Microprocessor virtualization extensions offer
new instructions to control virtualization. Operating systems provide
different levels of access to resources, called a protection ring. This ring
is a hierarchical level of privilege within the architecture of a computer
system. The most privileged layer is usually zero. Ring 0 not only has the
most privileges but also is the layer which directly accesses the system's
hardware.
In the traditional x86
architecture, operating system
kernels expect
direct CPU access running in Ring 0, which is the most privileged level. With
software virtualization, guest operating systems cannot run in Ring 0 because the VMM sits there.
The guest operating systems must therefore run in Ring 1, but there's a catch: Some x86
instructions work only in Ring 0, so the operating systems must be recompiled to avoid them.
This process is called
paravirtualization,
and it is impractical — especially if the
source code for the OS is not available.
To get around this, VMMs traps these instructions and emulates them, which
unfortunately results in an enormous performance hit: Virtual machines can
be significantly slower than real physical ones.
Thus, Intel and AMD have introduced their new virtualization technologies, a
handful of new instructions and — crucially — a new privilege level. The
hypervisor can now run at "Ring -1"; so the guest operating
systems can run in Ring 0.
There's no need for
paravirtualization, the
VMM
does less work, and the performance hit is reduced. Summing it Up: Compatibility &
Performance
The virtualization technologies offered by Intel and AMD are not
compatible, but each offers similar functionality. For reference saks, they
also are collectively referred to as hardware virtualization technology
(hardware VT or just VT). These
virtualization-friendly extensions for the x86 architecture essentially
provide the foundation to maximize the efficiency and capabilities of
software virtualization. Hardware VT performance is noted through the increase in the number of
virtual machines within a single physical system. Additionally there can be
larger numbers of users on the multiple virtual machines.
Because is is a relatively new technology, not all
virtualization software currently takes advantage of Intel and
AMD's virtualization technology, and you may
also find that the software supports only one and not both technologies. You
can, however, expect the major players in the virtualization software market
to support hardware-assisted virtualization.
For more terms and related links, you can view
Webopedia's
Virtualization category.
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Did You Know...
Popek and
Goldberg.s 1974 paper establishes three essential
characteristics for system software to be considered a VMM:
-
Fidelity.
Software on the VMM executes identically to its execution on
hardware, barring timing effects.
-
Performance.
An overwhelming majority of guest instructions are executed
by the hardware without the intervention of the VMM.
-
Safety. The
VMM manages all hardware resources.
(POPEK, G. J., AND GOLDBERG, R. P. Formal requirements for
virtualizable third generation architectures.)
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Vangie 'Aurora' Beal
Writer, www.Webopedia.com
Last updated: April 20, 2007
ServerWatch:
Server Virtualization Goes Prime Time 
Virtualization technology is enjoying a period
of explosive growth at the moment, and increasing numbers of enterprises are
becoming virtualization converts. Research firm IDC estimates about 750,000
virtual servers were in operation in 2004, and it expects this to rise to more
than 5 million by 2009 . a compound annual growth rate of almost 50 percent.
Introducing AMD Virtualization
Next-Generation AMD Opteron processors are
designed to help end the .one server, one application. problem common in so many
enterprises today.
Intel
Virtualization Technology
This issue of the Intel Technology Journal
(Volume 10, Issue 3) reviews virtualization, especially Intel Virtualization
Technology (Intel VT). These seven technical papers describe the key
capabilities of virtualization on Intel.s hardware and software platforms and
the virtualization roadmap for both Intel Architecture and Intel Itanium
processors.
Intel
Virtualization Technology Web site
Intel's Web site section which provides
information and resources on Intel VT technology.
ServerWatch - Guide to Internet Servers
and Platforms
Includes ratings, industry news, extensive
reviews, and downloadable server software.
A Comparison of Software
and Hardware Techniques for x86 Virtualization (PDF)
The main technical contributions of this paper are (1) a review of VMware
Workstation.s software VMM, focusing on performance properties of the virtual
instruction execution engine; (2) a review of the emerging hardware support,
identifying performancetrade-offs; (3) a quantitative performance comparison of
a software and a hardware VMM.
An
Introduction to Virtualization
The purpose of this document can be informally
stated as follows: if you were to use virtualization in a an endeavor (research
or otherwise), here are some things to look at.
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EnterpriseNetworkingPlanet provides practical
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Open Networks Today
Networking news moves at a fast pace, and Open
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filters, discussions, and news feed links.
VMware: The Virtual Desktop, The
Virtual Server
Virtual computers are often better than real
ones. When I was younger and a systems analyst for IBM's System/370 mainframe,
all my work centered on virtual machines; thanks to the design of the mainframe
hardware, my software never "saw" the real hardware, but merely a VM image,
common to all System/370 models, that provided a consistent runtime environment
not only for me, but for hundreds of simultaneous user sessions. |
