2.5 Virtual Hard Disks

2.5.1 Part 1: A virtual lab
By Val Bakh Virtual is an IT term that refers to something imitating, not quite real, or something that isn’t quite what it seems. A virtual computer, also known as a virtual machine (VM), can be described as a software-based imitation or a physical computer. It can be used in many ways to mimic a physical computer. A VM can be turned off and on, shut down and restarted, and can even be reset and rebooted. A VM can have devices (virtual, ofcourse) that can be added, modified, or removed just like a real computer. One such device is the virtual hard disk (VHD). It is a.vhd format file that logically emulates physical disks. A VHD appears in Windows Explorer as another file. However, a VM makes a VHD look like a hard disk. It can be partitioned, created volumes on it, formatted the volumes, installed an operating system, and stored data.
Windows 7 and Windows Server 2008 R2 allow you to attach a VHD (virtual hard disk) to a physical computer. The VHD can then be used as an additional physical hard drive. This functionality has been added to the Disk Management console as well as the Diskpart command line tool. You can now install Windows 7 and Windows Server 2008 R2 on a VHD, and boot a physical machine from the VHD. It is possible to run Windows 7 and Windows Server 2008 R2 on physical computers that are not connected to a VHD, but it can lead to a performance penalty of approximately 20 percent. Think about all the possibilities you now have! You can create a VHD and pretend it’s a disk. Then, create another VHD within it. You can create another one within the second VHD. The limitations of the NTFS filesystem mean that theoretically, no. In reality, however? You can install Hyper-V on a Windows Server 2008 R2 computer. Create a virtual machine with VHD-based storage. Then, you can start the two-level nesting limit again. You can now achieve three-level nesting since the VHD is used as the starting point rather than a physical drive. For fun, you can connect to Hyper-V server via the network from within a VM and attach VHDs that serve as storage for another, provided that the other VM is off.
It sounds like a lot fun, doesn’t it? It’s like traveling into the future and helping your older self invent a time-machine. Then you bring it back into the present (which is actually the original present) so your younger (in actuality, the original) self can travel to the future, where it all-kind of-started. It can be quite confusing, as you can see. You shouldn’t use virtualization to have fun. Make sure you use them wisely.
Here’s one way to do it. Every IT professional needs a playground (some call it a “sandbox”)–a computer lab in which he or she can test the real working of things and design solutions that will improve the lives of mortals. The lab can be as large as a dozen computers depending on what you work with and your budget. Shelves, racks, desks, cables, monitors, keyboards, mice–you name it. You also need to keep track of the computer names that you have assigned to your computer in the morning. This environment, which was supposed to be a paradise for IT pros, can quickly become a nightmare. How much time are you wasting on reinstallations when you make a mistake or need a new plan?
Now, compare this “real lab” to a virtual one. It’s all done on one computer, which may seem expensive and powerful, but it’s just one computer instead of a sprawling lab of “real” computers. How is this possible?

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