Basics of Windows Virtualization

There are Many Choices Including VMware and Microsoft Hyper-V

Nov 7, 2009

Virtualization solutions such as VMware ESX and Microsoft Hyper-V allow users to run far more machines than their budget could afford from buying extra computer servers.

The myraid of virtualization options available on the Windows platform are endless: Microsoft Virtual Server, VMWare Server, VMware ESX, VMWare ESXi, Microsoft Hyper-V, vMotion, hypervisors, guest operating systems. It can be very confusing trying to pick out what to use.

Virtualization has a lot of potential. If done properly, less hardware can be bought in exchange for a manageable layer of complexity. If improperly implemented, any potential savings from virtualization can be wiped out quickly. That's why it's important to choose the right virtualization product and implement it correctly.

Guest Operating System vs. Hypervisors

Guest operating systems require a host for the virtualization software. VMWare Server and Microsoft's Virtual Sever are two host-based virtualization solutions. They are best for small scale testing, such as developers' and programmers' workstations. Ideally, no more than one or two virtualized machines should be used due to the overhead it causes to the host system.

Hypervisor virtualization software solution, on the other hand, add a tiny layer of software between the computer hardware and the virtual machine. The overhead from running a full featured operating system goes away with hypervisor software. This allows hypervisor based solutions to scale to higher numbers of virtual machines with better performance. Microsoft's Hyper-V uses a miniature host operating system along wtih the hypervisor. VMWare's ESX uses just the hypervisor to manage the connection between the hardware and the virtual machine.

Memory Usage in Virtualization

An important consideration is how memory is used. In production environments, it's very important to make sure the virtual machines do not run out of RAM and begin to swap. When implementing a virtualization solution, each virtual machine should have an adequate amount of RAM to sustain simultaneous peak usage between all of the virtual machines available on the server.

With VMware, it's possible to commit more RAM than the amount available in the server. That sounds bad but it's really an advantage if done properly. If a virtual machine only needs extra memory during certain times of the day, it can borrow the RAM from another virtual machine temporarily.

Maximum Number of Virtual Machines

At Microsoft IT, where they are converting to 50% of servers to run virtual machines on Hyper-V, they are able to get 10.4 virtual machines per server which with four CPU sockets and 16 to 24 cores. However, Microsoft IT virtualization project states that these virtual machines have very low utilization, so the actual number is lower most customers can expect in real world usage is lower.

This underscores the need for testing and benchmarks in deciding how many virtual machines can support a given piece of computer hardware despite the specs of the virtualization solution. Nevertheless, the price of virtualization is far less than the cost of a new server. For the price of the virtualization software, an extra CPU or two, and extra RAM, a customer can run far more machines than they ever could before.

The copyright of the article Basics of Windows Virtualization in PC Software/OS is owned by John Wu. Permission to republish Basics of Windows Virtualization in print or online must be granted by the author in writing.