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Virtual Server 2005 (VS2005) allows a server to run multiple
operating systems or multiple copies of the same operating system at a single
time. On servers running Windows
Server 2003 and Virtual Server 2005, you can install multiple domain
controllers in separate virtual machines. For many organizations, the only
reason to use two separate servers to perform domain controller functions is to
provide redundancy in the event of the failure of one of the two servers.

Microsoft doesn’t necessarily recommend running these
critical functions on virtual servers in a production environment. However,
doing so can help your organization save money on server hardware by better using
its existing resources.

But this solution does involve some drawbacks that you
should consider. For example, when used improperly, this solution could mean
risking forest-wide Active Directory corruption.

In addition, you can expect a domain controller running
inside a VS2005-hosted virtual server to take a 30 to 50 percent performance
hit. This occurs in part because these machines can’t use multiple host
processors. From a security perspective, anyone who gains access to the virtual
hard disk image file could potentially misuse the information.

For more information, check out Microsoft’s “Running
Domain Controllers in Virtual Server 2005.”