Among the leading business challenges confronting CIOs and IT managers today are: cost-effective utilisation of IT infrastructure; responsiveness in supporting new business initiatives;and flexibility in adapting to organisational changes. Driving an additional sense of urgency is the continued climate of IT budget constraints and more stringent regulatory requirements. Virtualisation is a fundamental technological innovation that allows skilled IT managers to deploy creative solutions to such business challenges.
Virtualisation in a NutshellSimply put, virtualisation is an idea whose time has come. The term virtualisation broadly describes the separation of a resource or request for a service from the underlying physical delivery of that service. With virtual memory, for example, computer software gains access to more memory than is physically installed, via the background swapping of data to disk storage. Similarly, virtualisation techniques can be applied to other IT infrastructure layers - including networks, storage, laptop or server hardware, operating systems and applications. This blend of virtualisation technologies - or virtual infrastructure - provides a layer of abstraction between computing, storage and networking hardware, and the applications running on it (see Figure 1). The deployment of virtual infrastructure is non-disruptive, since the user experiences are largely unchanged. However, virtual infrastructure gives administrators the advantage of managing pooled resources across the enterprise, allowing IT managers to be more responsive to dynamic organisational needs and to better leverage infrastructure investments. Figure 1: Virtualisation Using virtual infrastructure solutions such as those from VMware, enterprise IT managers can address challenges that include: • Server Consolidation and Containment – Eliminating ‘server sprawl’ via deployment of systems as virtual machines (VMs) that can run safely and move transparently across shared hardware, and increase server utilisation rates from 5-15% to 60-80%. • Test and Development Optimisation – Rapidly provisioning test and development servers by reusing pre-configured systems, enhancing developer collaboration and standardising development environments. • Business Continuity – Reducing the cost and complexity of business continuity (high availability and disaster recovery solutions) by encapsulating entire systems into single files that can be replicated and restored on any target server, thus minimising downtime. • Enterprise Desktop – Securing unmanaged PCs, workstations and laptops without compromising end user autonomy by layering a security policy in software around desktop virtual machines. Virtualisation ApproachesWhile virtualisation has been a part of the IT landscape for decades, it is only recently (in 1998) that VMware delivered the benefits of virtualisation to industry-standard x86-based platforms, which now form the majority of desktop, laptop and server shipments. A key benefit of virtualisation is the ability to run multiple operating systems on a single physical system and share the underlying hardware resources – known as partitioning. Today, virtualisation can apply to a range of system layers, including hardware-level virtualisation, operating systemlevel virtualisation, and high-level language virtual machines. Hardware-level virtualisation was pioneered on IBM mainframes in the 1970s, and then more recently Unix/RISC system vendors began with hardware-based partitioning capabilities before moving on to software-based partitioning. For Unix/RISC and industry-standard x86 systems, the two approaches typically used with software-based partitioning are hosted and hypervisor architectures (See Figure 2). A hosted approach provides partitioning services on top of a standard operating system and supports the broadest range of hardware configurations. In contrast, a hypervisor architecture is the first layer of software installed on a clean x86-based system (hence it is often referred to as a “bare metal” approach). Since it has direct access to the hardware resources, a hypervisor is more efficient than hosted architectures, enabling greater scalability, robustness and performance. Figure 2: Virtualisation Architectures Hypervisors can be designed to be tightly coupled with operating systems or can be agnostic to operating systems. The latter approach provides customers with the capability to implement an OS-neutral management paradigm, thereby providing further rationalisation of the data center. Application-level partitioning is another approach, whereby many applications share a single operating system, but this offers less isolation (and higher risk) than hardware or software partitioning, and limited support for legacy applications or heterogeneous environments. However, various partitioning techniques can be combined, albeit with increased complexity. Hence, virtualisation is a broad IT initiative, of which partitioning is just one facet. Other benefits include the isolation of virtual machines and the hardware-independence that results from the virtualisation process. Virtual machines are highly portable, and can be moved or copied to any industry-standard (x86-based) hardware platform, regardless of the make or model. Thus, virtualisation facilitates adaptive IT resource management, and greater responsiveness to changing business conditions (see Figures 3-5). To provide advantages beyond partitioning, several system resources must be virtualised and managed, including CPUs, main memory, and I/O, in addition to having an inter-partition resource management capability. While partitioning is a useful capability for IT organisations, true virtual infrastructure delivers business value well beyond that. Figure 3: Traditional Infrastructure Figure 4: Virtual Infrastructure Figure 5: VMware Virtual Infrastructure 
Virtualisation for Server Consolidation and ContainmentVirtual infrastructure initiatives often spring from data center server consolidation projects, which focus on reducing existing infrastructure “box count”, retiring older hardware or life-extending legacy applications. Server consolidation benefits result from a reduction in the overall number of systems and related recurring costs (power, cooling, rack space, etc.) While server consolidation addresses the reduction of existing infrastructure, server containment takes a more strategic view, leading to a goal of infrastructure unification. Server containment uses an incremental approach to workload virtualisation, whereby new projects are provisioned with virtual machines rather than physical servers, thus deferring hardware purchases. It is important to note that neither consolidation nor containment should be viewed as standalone exercise. In either case, the most significant benefits result from adopting a total cost of-ownership (TCO) perspective, with a focus on the ongoing, recurring support and management costs, in addition to onetime, up-front costs. Data center environments are becoming more complex and heterogeneous, with correspondingly higher management costs. Virtual infrastructure enables more effective optimisation of IT resources, through the standardisation of data center elements that need to be managed. Partitioning alone does not deliver server consolidation or containment, and in turn consolidation does not equate to full virtual infrastructure management. Beyond partitioning and basic component-level resource management, a core set of systems management capabilities are required to effectively implement realistic data center solutions (see Figure 6). These management capabilities should include comprehensive system resource monitoring (of metrics such as CPU activity, disk access, memory utilisation and network bandwidth), automated provisioning, high availability and workload migration support. Figure 6: Virtual Infrastructure Management 
How Virtualisation Complements New-Generation HardwareExtensive ‘scale-out’ and multi-tier application architectures are becoming increasingly common, and the adoption of smaller form-factor blade servers is growing dramatically. Since the transition to blade architectures is generally driven by a desire for physical consolidation of IT resources, virtualisation is an ideal complement for blade servers, delivering benefits such as resource optimisation, operational efficiency and rapid provisioning. The latest generation of x86-based systems feature processors with 64-bit extensions supporting very large memory capacities. This enhances their ability to host large, memory-intensive applications, as well as allowing many more virtual machines to be hosted by a physical server deployed within a virtual infrastructure. The continual decrease in memory costs will further accelerate this trend. Likewise, the forthcoming dual-core processor technology significantly benefits IT organisations by dramatically lowering the costs of increased performance. Compared to traditional single-core systems, systems utilising dual-core processors will be less expensive, since only half the number of sockets will be required for the same number of CPUs. By significantly lowering the cost of multi-processor systems, dual-core technology will accelerate data center consolidation and virtual infrastructure projects, Beyond these enhancements, VMware is also working closely with both Intel and AMD to ensure that new processor technology features are exploited by virtual infrastructure to the fullest extent. In particular, the new virtualisation hardware assist enhancements (Intel’s “VT” and AMD’s “Pacifica”) will enable robust virtualisation of the CPU functionality. Such hardware virtualisation support does not replace virtual infrastructure, but allows it to run more efficiently. Para-virtualisation Although virtualisation is rapidly becoming mainstream technology, the concept has attracted a huge amount of interest, and enhancements continue to be investigated. One of these is para-virtualisation, whereby operating system compatibility is traded off against performance for certain CPU-bound applications running on systems without virtualisation hardware assist (see Figure 7). The para-virtualised model offers potential performance benefits when a guest operating system or application is ‘aware’ that it is running within a virtualised environment, and has been modified to exploit this. One potential downside of this approach is that such modified guests cannot ever be migrated back to run on physical hardware. In addition to requiring modified guest operating systems, paravirtualisation leverages a hypervisor for the underlying technology. In the case of Linux distributions, this approach requires extensive changes to an operating system kernel so that it can coexist with the hypervisor. Accordingly, mainstream Linux distributions (such as Red Hat or SUSE) cannot be run in a paravirtualised mode without some level of modification. Likewise, Microsoft has suggested that a future version of the Windows operating system will be developed that can coexist with a new hypervisor offering from Microsoft. Yet para-virtualisation is not an entirely new concept. For example, VMware has employed it by making available as an option enhanced device drivers (packaged as VMware Tools) that increase the efficiency of guest operating systems. Furthermore, if and when para-virtualisation optimisations are eventually built into commercial enterprise Linux distributions, VMware’s hypervisor will support those, as it does all mainstream operating systems. | 
