So how do you reduce the time it takes to build out complex lab environments? You may find it easier to build one Parent Disks for your OS i.e. Windows 2003 Server with SP1, and then save as a template or Parent disk. This will allow you to quickly build your lab without building a new server OS for each virtual instance.
Using differencing disks as described by Microsoft
http://technet2.microsoft.com/WindowsServer/en/Library/d9ef5bd9-6ca2-488b-a960-f3f8ecd6ecc51033.mspx
You can associate more than one differencing disk to one parent, which means that virtual machines can share one parent disk but have their own differencing disk. This way of using differencing disks can be useful in a variety of scenarios. For example, a test engineer or call center technician could have a dozen or more virtual machines with different configurations, such as allocated memory or type of networking, with different software updates, and different installed applications. The virtual machines could share a parent disk that contains the operating system, and each virtual machine could have its own differencing disk to store the configuration that differs from the parent.
If you use multiple differencing disks that share a parent disk containing an operating system, you must apply any software updates to each differencing disk. If you applied the software update to the parent disk, all differencing disks associated with that parent disk would be unusable.
You can chain differencing disks, which means that a differencing disk can have another differencing disk as a parent disk. Depending on how you design the chain, you can save considerable disk space. For example, if you want to test upgrade scenarios or version compatibility, you could use a parent disk as the base and a chain of differencing disks for the consecutive versions. This approach would save disk space if each differencing disk contained one update only.
Remember to protect the OS Parent by always setting it to read only. To create a differencing disk from a Parent disk perform the following, and then use the differencing disk as the existing virtual hard disk when creating the Virtual Machine. Note the differencing disk will always start off as 37KB and then grow when configured as the hard disk for a Virtual Instance and is then turned on.
To create a differencing virtual hard disk as found under Virtual Server 2005 Help
- In the navigation pane, under Virtual Disks, point to Create and then click Differencing Virtual Hard Disk.
- In Location, select the folder in which to store the virtual hard disk file. If the folder you want does not appear in the list, you must type the fully qualified path to the folder in the following step.
- In Virtual hard disk file name, after the path to the folder, type a name for the differencing virtual hard disk that you want to create. You do not need to include a file name extension.
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Do one of the following:
- In the Known virtual hard disks box (in the lower part of the page), select the virtual hard disk file to use as the parent.
- If the virtual hard disk file that you want does not appear in the Known virtual hard disks list, in Fully qualified path to parent virtual hard disk, type the fully qualified path to the virtual hard disk file.
- Click Create.
Some additional help will be provided by two very useful utilities known as NewSID and BGInfo
I personally place these two utilities on every Parent Disk I create of NT 4 through Windows 2003.
NewSID
http://www.sysinternals.com/utilities/newsid.html
Newsid provides a quick and easy way to Re-Sid the differencing disk once online as well as rename the machine.
BGInfo
http://www.sysinternals.com/utilities/bginfo.html
Bginfo is ideal for labeling the desktop in what role, name, and IP settings the server has.
