Eight types of virtualization:
Operating System Virtualization - The most prevalent form of virtualization today, virtual operating systems (or virtual machines) are quickly becoming a core component of the IT infrastructure. Generally, this is the form of virtualization end-users are most familiar with. Virtual machines are typically full implementations of standard operating systems, such as Windows Vista or RedHat Enterprise Linux, running simultaneously on the same physical hardware. Virtual Machine Managers (VMMs) manage each virtual machine individually; each OS instance is unaware that 1) it’s virtual and 2) that other virtual operating systems are (or may be) running at the same time. Companies like Microsoft, VMware, Intel, and AMD are leading the way in breaking the physical relationship between an operating system and its native hardware, extending this paradigm into the data center.
Application Server Virtualization - The core concept of application server virtualization is an appliance or service that provides access to many different application services transparently. In a typical deployment, a reverse proxy will host a virtual interface accessible to the end user on the “front end.” On the “back end,” the reverse proxy will load balance a number of different servers and applications such as a web server. One server is presented to the world, hiding the availability of multiple servers behind a reverse proxy appliance. Application Server Virtualization can be applied to any (and all) types of application deployments and architectures, from fronting application logic servers to distributing the load between multiple web server platforms, and even all the way back in the data center to the data and storage tiers with database virtualization.
Application Virtualization - While they may sound very similar, Application Server and Application Virtualization are two completely different concepts. What we now refer to as application virtualization we used to call “thin clients.” The technology is exactly the same. The local laptop provides the CPU and RAM required to run the software, but nothing is installed locally on your own machine. Other types of Application Virtualization include Microsoft Terminal Services and browser-based applications.
Management Virtualization - If you implement separate passwords for your root/administrator accounts between your mail and web servers, and your mail administrators don’t know the password to the web server and vise versa, then you’ve deployed management virtualization in its most basic form. The paradigm can be extended down to segmented administration roles on one platform or box, which is where segmented administration becomes “virtual.” User and group policies in Microsoft Windows XP, 2003, and Vista are an excellent example of virtualized administration rights.
Network Virtualization - A simple example of IP virtualization is a VLAN: a single Ethernet port may support multiple virtual connections from multiple IP addresses and networks, but they are virtually segmented using VLAN tags. Each virtual IP connection over this single physical port is independent and unaware of others’ existence, but the switch is aware of each unique connection and manages each one independently.
Hardware Virtualization - Hardware virtualization is very similar in concept to OS/Platform virtualization, and to some degree is required for OS virtualization to occur. Hardware virtualization breaks up pieces and locations of physical hardware into independent segments and manages those segments as separate, individual components. Although they fall into different classifications, both symmetric and asymmetric multiprocessing are examples of hardware virtualization. In both instances, the process requesting CPU time isn’t aware which processor it’s going to run on; it just requests CPU time from the OS scheduler and the scheduler takes the responsibility of allocating processor time. As far as the process is concerned, it could be spread across any number of CPUs and any part of RAM, so long as it’s able to run unaffected.
Storage Virtualization - Storage virtualization can be broken up into two general classes: block virtualization and file virtualization. Block virtualization is best summed up by Storage Area Network (SAN) and Network Attached Storage (NAS) technologies: distributed storage networks that appear to be single physical devices.
Most file virtualization technologies sit in front of storage networks and keep track of which files and directories reside on which storage devices, maintaining global mappings of file locations.
Service Virtualization - Service virtualization is consolidation of all of the above definitions into one catch-all catchphrase. Service virtualization connects all of the components utilized in delivering an application over the network, and includes the process of making all pieces of an application work together regardless of where those pieces physically reside.
