Computer hardware virtualization has been in vogue for nearly two decades now, but many folks still have a tough time understanding what it’s all about. The maturity of the concept, however, makes it pretty much a no-brainer for any business or government agency that needs more than a couple of servers.
The fundamental tenet of virtualization is that computers rarely utilize all their allocated resources. Let’s use memory as an example. A typical Windows server is configured with 8 GB of RAM but rarely uses all of it. Typically it will use the full 8 GB only a small percentage of the time. This is where virtualization can help.
A host server can run several Windows machines, known as guests. Following our example, let’s say we configure a host with 24 GB of RAM, and we run six Windows guest machines on it. Instead of equally dedicating the 24 GB among the six guests, the host tricks each Windows machine into thinking it has 8 GB of RAM. Because each Windows machine rarely uses the full 8 GB, the 24 GB is sufficient to run all six machines. This trickery is the basis of all types of virtualization.
This concept is extended to CPU as well. A typical Windows server rarely uses the full power of the CPU. As such the CPU can be shared among several guest machines.
Of course, there is a limit to the number of times a resource can be virtualized. This is best illustrated when considering storage. Let’s say we have 4 TB of hard disk space, and we allocate it among the six guest machines. We trick the guests into thinking they have 1 TB each, gambling that not all of them will use the full amount. But we have a hard limit of 4 TB, and if we hit that limit, bad things happen.
Figuring out how to divvy up the resources without oversubscribing them can be challenging. There are formulas available for typical workloads, and all contemporary virtualization platforms allow adjustment of the allocations after implementation.
When it comes to vendors, the most popular is VMware. Basically first to the virtualization mass market, VMware’s flagship ESXi is mature and the favorite of most systems administrators. In second is Hyper-V, Microsoft’s offering, which has been on the market for about a decade now.
Both ESXi and Hyper-V have free versions which are great for small environments. Hyper-V is actually built into Windows Server, but licenses must be purchased for larger environments.
Virtualization is not limited to servers; desktops can be virtualized as well. VDI (virtual desktop infrastructure) is typically appropriate for larger environments and presents a variety of different challenges, but that’s a topic for another column.
John Agsalud is an IT expert with more than 25 years of information technology experience in Hawaii and around the world. He can be reached at jagsalud@live.com.
