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This can be where confusions creep in so it is important to remember the fundamental concept of virtualization (and again I refer to the article, The Fundamental Concept of Virtualization, on this website): It represents an abstraction from physical resources. All uses of virtualization are centered around this concept.

There are three major types of virtualization:

1. Server Virtualization

   This type is where most of the attention is focused right now in the world of virtualization and is where most companies begin an implementation of this technology. That’s not very shocking in light of the fact that server sprawl has become a very large and legitimate problem in enterprises throughout the world. Where a company is simply running out of room in which to place all of their servers, this type of virtualization would of course get viewed with strong interest.

   Because each server typically serves one function (i.e., mail server, file server, Internet server, enterprise resource planning server, etc.), with each server using only a fraction of its true processing power, server virtualization breaks through the “one application, one server” barrier and facilitates the consolidation of numerous servers into one physical server. This equates to (a) less physical servers required, and (b) 70 to 80 percent or higher utilization of existing hardware as opposed to the previous 10 to 15 percent.

   Server virtualization lets one server do the job of multiple servers by sharing the resources of a single server across multiple environments. The software lets a company host multiple operating systems and multiple applications locally and in remote locations, freeing users from physical and geographical limitations.

   How are the servers moved over?

   Most, if not all, virtualization solutions offer a migration tool to take an existing physical server and make a virtual hard drive image of that server to the driver stack. Then that server will boot up and run as a virtual server. There is no need to rebuild servers or manually reconfigure them as a virtual server.

   Without a doubt, the greatest advantage of server virtualization is cost. In addition to energy savings and lower capital expenses due to more efficient use of hardware resources, you get high availability of resources, better management, and improved disaster-recovery processes with a virtual infrastructure. You save on physical space, reduce power consumption and the need for as much cooling, and are able to rapidly deploy a new application without ordering new hardware.

   There are three different methods that can be employed under the server virtualization category but I’m not going to get into them right now because I’m trying very hard to be as simple about this as I can possibly be. Whichever method is used, the goal of server consolidation is the same.

2. Client (or Desktop) Virtualization

   This type of virtualization technology has to do with a client (a workstation desktop or laptop pc – an end user machine). These can be very difficult for a systems administrator to manage. Whereas any machine in the company’s data center has very strict procedures regarding what gets loaded on them and when they get updated with new software releases, it is often a quite different scene when it comes to the end-user machine. Even if there are supposed to be procedures followed for the above actions on an end-user machine, those procedures are often not followed or paid much heed. A CD or DVD slot makes it easy for non-approved software to be installed that can create problems on that machine. Quite aside from that, end-user machines are more susceptible to malware in numerous ways – via e-mail viruses, unwitting spyware downloads, etc. Last but not least, most end-user machines run on Microsoft Windows which is well known for attracting attacks from hackers and cybercriminals.

   IT has to not only deal with all those problems but also attend to the normal problems inherent in client machines: keeping approved software up-to-date, patching the OS, keeping virus definitions current, et al.

   All of these factors make an IT guy’s job quite challenging. So client virtualization, with the hope of easier client machine management and security, attracts the interest of IT.

   Because there is no single solution for end-user computing, there is more than one method or model that can be employed:

   1. Remote (Server-Hosted) Desktop Virtualization

      In this model, the operating environment is hosted on a server in the data center and accessed by the end user across a network.

   2. Local (Client-Hosted) Desktop Virtualization

      In this model, the operating environment runs locally on the user’s physical pc hardware and involves multiple flavors of client-side virtualization techniques that can monitor and protect the execution of the end user system.

   3. Application Virtualization

      This is a method of providing a specific application to an end user that is virtualized from the desktop OS and which is not installed in a traditional manner. An application can be installed and/or executed locally within a container that controls how it interacts with other system and application components. Or an application can be isolated in its own virtualized “sandbox” to prevent interaction with other system and application components. Or applications can be streamed across a network. Or applications can be delivered across the network to a web browser with most processing executed on a centralized web server. This latter method will support almost any user, with no installation requirement, on almost any platform, in any location, but it only supports a limited set of applications.

3. Storage Virtualization

   Storage virtualization is a concept in System Administration, referring to the abstraction (separation) of logical storage (virtualized partitions of stored data) from physical storage (storage devices that hold, spin, read and write magnetic or optical disks such as CD, DVD, or even a hard disk drive, etc.). This separation allows the Systems Admin increased flexibility in how they manage storage for end users.

   Virtualization of storage helps achieve location independence by abstracting the physical location of the data. The virtualization system presents to the user a logical space for data storage and itself handles the process of mapping it to the actual physical location.

   There are three basic approaches to data storage:

   1. Direct-Attached Storage (DAS)

      This is the traditional method used in data storage where hard drives are attached to a physical server. Because this method is easy to use but hard to manage, virtualization technology is causing organization to have a second thought with regard to its viability.

   2. Network-Attached Storage (NAS)

      This is a machine that resides on your network and provides data storage to other machines. It can be thought of as the first step toward storage virtualization. This approach provides a single source of data, facilitating data backup. By collecting your data in one place, it also avoids the problem of multiple servers needing to access data located on another server.

   3. Storage Area Network (SAN)

      This ultra-sophisticated approach deploys specialized hardware and software to transform mere disk drives into a data storage solution that transfers data on its own high-performance network.

      Companies shift over to a SAN when they recognize that corporate data is a key resource that must be available 24/7 and needs to be conveniently managed. The price tag for this approach is very high indeed.

   SHARING IS EASY!