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Fahmi Rizwansyah says:

Virtualization Management
Virtualization technologies can deliver sea-changing benefits to your organization. But, as Thomas Bittman, Gartner analyst, adroitly noted, "Virtualization without good management is more dangerous than not using virtualization in the first place."
As an organization's computing environment gets more virtualized, it also gets more abstract. Increasing abstraction can increase complexity, making it harder for IT staff to control their world and undermining the benefits of virtualization.

Integrating physical and virtual management enables you to realize the full promise of virtualization while minimizing its risks. An integrated approach is critical because all IT infrastructures—even those with a significant amount of virtualization—include both virtual and physical components. Even if you have a management system that effectively handles virtualized systems, if it doesn't manage physical systems you will still have to manage many separate "islands"—and you will consume much more time and resources than you would with a management system that can handle all your assets. By using comprehensive virtualization management technology, you keep complexity at a minimum and streamline operations. A common virtualization management environment reduces training, ensures uniform policy application and simplifies maintenance.

Effective physical and virtual management can optimize the benefits of using virtualization technologies. This includes monitoring and managing hardware and software in a distributed environment. By allowing operations staff to monitor both the software running on physical machines and the physical machines themselves, it lets them know what's happening in their environment. It also lets them respond appropriately, running tasks and taking other actions to fix problems that occur.

Another unavoidable concern for people who manage virtualized, distributed environments is installing software and managing how that software is configured. While it's possible to perform these tasks by hand, end-to-end virtualization management technology can automate and accelerate this process.

Tools that work in both the physical and virtual worlds are highly effective and attractive. Yet think about an environment that has dozens or even hundreds of VMs installed. How are these machines built, changed and depreciated? And how are other VM-specific management functions performed? Addressing these questions requires a comprehensive toolset that includes managing virtualized hardware. Among other benefits, it can help operations staff choose workloads for virtualization, create the VMs that will run those workloads, and transfer the applications to their new homes.

Server Virtualization
For most IT people, the word "virtualization" conjures up thoughts of running multiple operating systems on a single physical machine. This is hardware virtualization, and while it's not the only important kind of virtualization, it is unquestionably the most visible today.
The core idea of hardware virtualization is simple: Use software to create a virtual machine that emulates a physical computer. This creates a separate OS environment that is logically isolated from the host server. By providing multiple VMs at once, this approach allows running several operating systems simultaneously on a single physical machine.

Rather than paying for many under-utilized server machines, each dedicated to a specific workload, server virtualization allows consolidating those workloads onto a smaller number of more fully-used machines. This implies fewer people to manage those computers, less space to house them, and fewer kilowatt hours of power to run them, all of which saves money.
Server virtualization also makes restoring failed systems easier. VMs are stored as files, and so restoring a failed system can be as simple as copying its file onto a new machine. Since VMs can have different hardware configurations from the physical machine on which they're running, this approach also allows restoring a failed system onto any available machine. There's no requirement to use a physically identical system.

Application Virtualization
In a physical environment, every application depends on its OS for a range of services, including memory allocation, device drivers, and much more. Incompatibilities between an application and its operating system can be addressed by either server virtualization or presentation virtualization. But for incompatibilities between two applications installed on the same instance of an OS, you need application virtualization.
Applications installed on the same device commonly share configuration elements, yet this sharing can be problematic. For example, one application might require a specific version of a dynamic link library (DLL) to function, while another application on that system might require a different version of the same DLL. Installing both applications creates a situation, where one of them overwrites the version required by the other causing the application to malfunction or crash. To avoid this, organizations often perform extensive compatibility testing before installing a new application, an approach that's workable but quite time-consuming and expensive.

Application virtualization solves this problem by creating application-specific copies of all shared resources. The configurations an application might share with other applications on its system—registry entries, specific DLLs, and more—are instead packaged with it and execute in the machine's cache, creating a virtual application. When a virtual application is deployed, it uses its own copy of these shared resources.
Application virtualization makes deployment significantly easier. Since applications no longer compete for DLL versions or other shared aspects of their environment, there's little need to test new applications for conflicts with existing applications before they're rolled out. And these virtual applications can run alongside ordinary, installed applications—so not everything needs to be virtualized, although doing so avoids many problems and decreases the time end-users spend with the helpdesk trying to resolve them. An effective application virtualization solution also enables you to manage both virtual applications and installed applications from a common interface.

Storage Virtualization
Generally speaking, storage virtualization refers to providing a logical, abstracted view of physical storage devices. It provides a way for many users or applications to access storage without being concerned with where or how that storage is physically located or managed. It enables the physical storage in an environment to be shared across multiple application servers, and physical devices behind the virtualization layer to be viewed and managed as if they were one large storage pool with no physical boundaries.

Virtualizing storage networks enables two key additional capabilities:
* The ability to mask or hide volumes from servers that are not authorized to access those volumes, providing an additional level of security.
* The ability to change and grow volumes on the fly to meet the needs of individual servers.

Essentially, anything other than a locally attached disk drive might be viewed in this light. Typically, storage virtualization applies to larger SAN (storage area network) arrays, but it is just as accurately applied to the logical partitioning of a local desktop hard drive, redundant array of independent disks (RAID), volume management, virtual memory, file systems and virtual tape. A very simple example is folder redirection in Windows, which lets the information in a folder be stored on any network-accessible drive. Much more powerful (and more complex) approaches include SANs. Large enterprises have long benefited from SAN technologies, in which storage is uncoupled from servers and attached directly to the network. By sharing storage on the network, SANs enable highly scalable and flexible storage resource allocation, high efficiency backup solutions, and better storage utilization.

Cheers, frizzy2008.