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What Is Server Virtualization And Why Use It?

By Brian Jensen, Dell

With technology budgets getting tighter, the advantages of running a number of operating systems and server functions virtually on one physical server instead of several can be compelling. Brian Jensen at Dell explains how virtualization can squeeze the maximum performance out of your hardware.

Most servers only use a small fraction of their overall processing capabilities. Another problem is that when a computer network gets bigger and more complex, the servers take up a lot of physical space causing a data centre to become overcrowded with racks of servers that consume a lot of power and generate a significant amount of heat. Server virtualization addresses both of these issues in one fell swoop. By using specially designed software, an administrator can convert one physical server into multiple virtual machines.

Multiple Operating Systems on One Computer

Server virtualization is a method of running multiple autonomous virtual operating systems on just one physical computer. It is an effective approach to maximizing both physical resources and the investment in hardware. Using the principle of virtualization, it is now possible to turn an inexpensive commodity server into 15 virtual servers running 15 virtual operating systems. (Dell's site has more information on virtualization and virtual servers.)

When does Server Virtualization Make Sense?

Virtualization is usually an ideal solution for applications such as Microsoft Exchange Server or interoffice file sharing and those that are meant for small or medium-scale usage. As a business grows, it is important to keep in mind that server virtualization is not recommended for use with high-performance applications where servers must be clustered together to meet performance requirements of just one application. In these situations the added overhead and complexity would reduce performance. Many industry experts suggest that you never let a server exceed 50% CPU (processor) utilization during the peak loads.

Reasons to Use Server Virtualization

There are a multitude of reasons companies and organizations invest in server virtualization. While some of the reasons are financially motivated, others address technical concerns. Listed below are a few of those reasons:

Virtualization Lowers Acquisition and Maintenance Costs

Virtualization technology achieves higher server density while decreasing total computing power. This can greatly decrease many of the hardware acquisition and maintenance costs and result in significant savings for any company or organization. The key is to know when virtualization makes sense.

Server Virtualization Conserves Space

Virtualization conserves space through consolidation. By taking several applications that only use a small amount of processing power, the administrator of the network can consolidate several machines into one server that runs multiple virtual environments. This can result in a decreased need for physical space.

Reducing Service Interruptions

Server virtualization enables companies to practice redundancy without having to purchase additional hardware. Redundancy has reference to running the same application on multiple servers. This provides an important safety measure; when a server fails for any reason, another server running the same application simply takes its place.

Redundant Servers are Located on Separate Machines

This greatly reduces any interruption in service. It would not make sense to build two virtual servers that perform the same application on the same physical server. If that physical server were to crash, both of the virtual servers would obviously also fail. For this reason, network administrators usually create redundant virtual servers on separate physical machines.

Testing New Applications

Another benefit of virtual servers in large organizations is that they enable programmers isolated, independent systems in which they are able to test new applications and operating systems. Instead of buying a separate dedicated physical machine, the administrator can create a virtual server on one of the existing machines. Since each virtual server is independent from all the other servers in the network, programmers can run different software programs without worrying about adversely affecting other applications.

Types of Server Virtualization

There are essentially three ways to create virtual servers which are listed below:

  • Full virtualization
  • Paravirtualization
  • OS-level virtualization

All three of these methods of creating virtual servers share a few common traits. The physical server is referred to as the host. The virtual servers are referred to as guests. The virtual servers act like physical machines but each system uses a different approach in allocating physical server resources to the various virtual server needs.

Full Virtualization

With full virtualization a special type of software is used called hypervisor or VMM, Virtual Machine Management. Hypervisor interacts directly with the physical server's CPU and disk space. It acts as the platform for the virtual servers' operating systems. Commonly used software includes Microsoft’s Hyper-V and VMWare.

Virtual Servers Run Independently

The hypervisor software keeps each virtual server completely independent and unaware of other virtual servers running on the same physical machine. Every guest server runs on its own OS (operating system) - it is even possible to have a guest running on Linux and another on Windows.

Monitoring the Physical Servers Resources

The hypervisor software monitors the physical server's resources. As the virtual servers run applications, the hypervisor relays resources from the physical machine to the appropriate virtual servers. Hypervisors have their own processing needs. This means that the physical server must reserve processing power and resources for to running the hypervisor application. In some cases this may impact overall server performance and it can slow down applications.

Paravirtualization

Unlike the full virtualization, the guest servers in a paravirtualization system are aware of each other. Since the OS is already aware of the demands that the other operating systems are putting on the physical server, a paravirtualization hypervisor does not require as much processing power while managing guest operating system.

OS-level Virtualization

Hypervisor software is not utilized with the OS-level virtualization approach. The virtualization capability is part of the host OS. It performs all of the functions of a fully virtualized hypervisor. Perhaps the biggest limitation of this approach is that all of the guest servers are required to run the same OS. Although every virtual server remains independent from the others, you can't mix and match operating systems. This is referred to as a homogeneous environment because all of the guest operating systems must be the same.

Which Method is Better?

It is difficult to say that one of these methods is better than the other two because it really depends on the needs of the administrator. When the administrator's physical servers are all running on the same operating system, an OS-level approach may work best. OS-level systems often tend to be faster than other methods. If the administrator happens to be running servers on multiple operating systems, para-virtualization would possibly be a better choice.

Computer scientists have created virtual machines on supercomputers for many years and therefore, server virtualization is not a new concept. It is, however, only within recent history  that virtualization has become feasible for servers. It is still a young but rapidly growing area of technology and several companies offer innovative approaches.


About the author

Brian Jensen, Dell

Brian Jensen is Online Marketing Manager with Dell. He has a passion for learning and writing about all things technology and is currently learning more about Virtual Desktops.


Glossary

CPU, Hardware, Linux, Network, Operating System, Processor, Software

Published: 29th October 2021

Copyright © 2021 Brian Jensen, Dell

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