Introduction to Server Virtualization

What Is Virtualization? What Are the Benefits?

A typical data center contains many servers. Traditionally, since hardware was cheap and applications were complex, many administrators installed one application per server. Though this provided their applications with security and isolation from other processes, it resulted in server sprawl. Workload on these servers would vary widely depending on the time of day and user activity. Many of the servers would spend a large percentage of their time idling away, doing practically nothing. Average server utilization levels are typically about 10%. Server virtualization increases each physical machine’s utilization by dividing physical servers into multiple virtual servers. Each virtual server contains its own operating environment and applications; it looks and acts exactly like a real server.

There are three ways to run virtual servers: full virtualization, para-virtualization and OS-level virtualization. In all three, the physical server is called the host and the virtual servers are called guests.

Full virtualization uses a special kind of software called a hypervisor to supervise the guests. It interacts directly with the host’s CPU, disk and network access. The hypervisor keeps each of the guests independent of one another and unaware of the other servers running on the same machine. Full virtualization requires the most overhead, and thus allows the least number of virtual servers per physical server.

With para-virtualization, the guest servers are aware of each other’s existence. Though it also uses a hypervisor, para-virtualization doesn’t require as much overhead as full virtualization because the guests are each aware of the load that they’re placing on the host. This method requires that the host be running a specially modified version of the operating system to cooperate with the hypervisor, but it offers a considerable performance improvement over full virtualization.

An OS-level virtualization doesn’t have a hypervisor at all. The host’s operating system performs the hypervisor’s duties and interacts with the guests. The biggest drawback of OS-level virtualization is that all of the virtual servers must run the same operating system as their physical server, but the performance in the guests can be similar to an actual physical machine!

Which is best? It depends on the needs of the data center. If all the servers run the same operating system, the OS-level virtualization would be the fastest and allow the most virtual servers per host. If you need to combine a number of servers running different operating systems, both full virtualization and para-virtualization can do the job, but full virtualization is the older and more mature technology for doing so.

When to use Virtualization?

Virtualization is perfect for small to mid-size applications and services that don’t fully tax the hardware resources. Since virtualization is dividing a server’s resources into fractions, applications that are too resource-intensive can overwhelm the server. When the physical server can’t meet the demands of one of the virtual servers, all of the virtual servers will bog down.

Virtualization allows for server consolidation. If there are many applications that each only use a small amount of processing power, the administrator can consolidate several servers into one virtual machine. In a data center with hundreds or thousands of computers, the power and cooling savings would be significant.

In the past, when you upgraded your server hardware because it was obsolete, you were usually required to upgrade, or at the very least, extensively test all of the software running on it as well, because the old version of the software might not run the same on the new hardware. With virtualization, though, it is possible to maintain the same operating environment regardless of any changes to the physical infrastructure of the server. This has far-reaching implications for server upgrades, because upgrades are typically incredibly expensive, not just because of the cost of the actual hardware but because of the associated costs of testing to make sure that that everything behaves as it should. …
Read More »

Greening Your IT

Computer networks and the Internet have freed businesses of all sizes from many of the visible costs associated with intra-office communication. Gone are the days of fax machines and couriers. Today, a user at his desk can instantly send a 300 page report to his colleagues on the other side of the planet for next to nothing. Almost nothing, though, isn’t the same as free. There are real costs associated with transmitting emails, both in dollars and cents and in greenhouse gases.

McAfee, Inc. and the climate-change researchers from ICF International have calculated the amount of energy required to transmit, process, and filter all of the spam email sent worldwide for an entire year. Their results are astounding:

[the annual energy] totals 33 billion kilowatt-hours (kWh), or 33 terawatt hours (TWh). That’s equivalent to the electricity used in 2.4 million homes, with the same green house gas emissions as 3.1 million passenger cars using 2 billion gallons of gasoline.

Each spam message is responsible for, on average, 0.3 grams of CO2. That is the equivalent of driving your car three feet! Multiply that by the 358 spams I received yesterday and you’ll see the enormity of the situation. Non-spam email doesn’t have quite the same costs associated with it, because much of spam’s energy consumption comes from users deleting it and trying to find the legitimate email mixed amongst it. But, it does cost something.

Green computing is an effort to make networks and computers more energy efficient. Because corporate computer systems rely on wide variety of computers, networking equipment and employees, there are many techniques available to green up your IT infrastructure. One of the best options for greening your computer systems is to take advantage of virtualization technologies. Virtualization is the process by which software running on a computer is separated from the computer itself. …
Read More »