Remember, VMs consume resources just as physical servers do, so make sure you have enough RAM and hard disk resources on the host server to accommodate the number of VMs that you plan to run concurrently on the host. For example, if you plan to allocate 128MB of virtual RAM for each of three NT server VMs, you'll need to install 384MB of RAM in addition to the amount of memory that the host OS and its running applications require. Also, be sure to allocate enough disk space for each VM's virtual hard disks. You don't need to create separate partitions for the hard disks because the virtual hard disks are stored in files with .vhd file extensions.
After you've set aside enough resources for the VMs, you need to determine how to network them. You can either have them share the host computer's network adapter and directly connect to the production network, or you can configure them to use a virtual network that connects only to the host system. I prefer the latter approach primarily because it isolates the VMs from the physical systems on the production network. Also, creating a virtual network connection eliminates NetBIOS conflict errors during the migration process and lets you fully test and configure the VMs without affecting the physical production NT servers.
To set up a virtual network, you need to open the Control Panel Add/Remove Hardware applet on the host system to install the Microsoft Loopback Adapter. After you install the adapter, edit its TCP/IP settings to assign the first IP address to the adapter on a unique network, such as 10.1.0.1/24. When you install VMs on the host server, you can configure their network interfaces to use other IP addresses on the same virtual subnet.
Of course, a virtual network that can only be seen by the VM host is pointless if users can't access the virtual NT server. To facilitate user access while keeping all VMs on their own private network, I configure Routing and Remote Access on the host system to act as a network router. You can use the Microsoft Management Console (MMC) Routing and Remote Access Service snap-in to quickly set up this service by running the configuration wizard that appears after you first attempt to configure the service. To let any administrator access the virtual network and the live VMs, you can use the Route Add command to add static routes to the administrators' systems. For example, to access the virtual network 10.1.0.0/24 attached to a host system with an IP address of 172.16.12.34, you would run the command
route add p 10.1.0.0
mask 255.255.255.0 172.16.12.34
When you're ready to permanently transition all your VMs into production as replacements for the physical NT servers, you would just need to update the routing tables of your production routers, then modify each VM's A host records on the production DNS server.
If you don't want to go down the routing path, you can always configure your VMs' network interfaces to connect to one of the host system's physical network interfaces. This configuration would let the VMs connect directly to the production network and only require that their virtual network interfaces have a unique production IP address. If you take this approach, remember to isolate your VM from the production server that it's replacing so that you don't get NetBIOS errors, which would occur if the identical systems were able to see each other on the same physical network segment.
Adding VMs
After you've planned how much disk space and RAM to use for the VMs and configured the virtual networking on the host system, you can install the Virtual Server application by downloading and running the executable file, then setting up the VMs. To add VMs, you need to access the Virtual Server Master Status page—go to Start, Programs, Microsoft Virtual Server, then click the Master Status shortcut or point your Microsoft Internet Explorer (IE) 5.5 or later Web browser to http://host server name:1024/virtualserver/vswebapp/vswebapp.exe to access the Web management GUI, as Figure 2 shows.
After you access the Master Status page, you need to configure a virtual network for the virtual server to use. From the Tools menu, click Virtual Network Manager, then select Create Virtual Network. You'll need to name the virtual network and select the network from the Host Network Adapter drop-down menu to connect to the Microsoft Loopback Adapter on the host system.
You can now create a new VM. From the Tools menu, click Add Virtual Machine and allocate RAM and a virtual hard disk to the new VM. For its virtual network interface, in the Ethernet NIC field, select the virtual network that you just created. Then, click Create Virtual Machine to create the VM.
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