SCALABLE ENTERPRISE1.1.10.*1.1.20.*Virtual IP subnetVirtual IP subnet1.1.30.*1.1.40.*Virtual IP subnetVirtual IP subnet1.1.50.*1.1.60.*Virtual IP subnetVirtual IP subnet1.1.70.*1.1.80.*Virtual IP subnetVirtual IP subnet<strong>Power</strong>Edge 2650 <strong>Power</strong>Edge 2650Virtual machinesLinux routerWindows primary domain controllerWindows clientWindows backup domain controllerWindows DNS server Physical serverFigure 2. Virtualized network test environment for Active Directory clientvirtualization technology, some limitations exist. In all cases, thenumber of VMs that can be hosted depends on the physical capacityof the underlying server and the aggregate workload characterizationof the VMs. For this particular test case, engineers determinedthat between 10 and 20 VMs could easily coexist on a single<strong>Power</strong>Edge 2650 server. And this scenario presented an additionalconstraint: The product being tested is a physical hardware componentand must be installed in a nonvirtualized environment.Therefore, the systems on which the product under test was installedhad to be physical systems. However, the rest of the test bed, comprisingdomain controllers, client workstations, and network routers,did not have the same physical dependency and could be consolidatedonto two physical systems.Isolation. Because virtualization enables multiple, potentiallydifferent operating systems to run simultaneously on the samephysical server without side effects, the many types of systems foundin a heterogeneous network environment can be created virtually. Thedomain controllers for this test environment as well as client workstationswere hosted by virtualized Microsoft Windows 2000 Serversystems, and the network routers were virtualized Linux routers. Animportant aspect of this test environment is that the fact that thesesystems are virtualized is transparent to other servers, both virtualand physical. For all practical purposes—such as communicatingwith other virtual and physical systems—VMs have the appearanceand functionality of physical systems.Replication. For this scenario, test engineers needed to constructmany instances of domain controllers, client workstations, andnetwork routers. However, they needed to create only one “reference”software stack for each of these categories. Once built, eachreference stack was cloned simply by copying and then personalizingthe file with a configuration specifying details such as virtualmachine ID and network name. <strong>Dell</strong> engineers used this method tocreate as many instances of each component as needed.Figure 2 shows the implementation details for the virtual environmentused to test the Active Directory client product. Physicalservers on which the product was installed are indicated along theright and left sides of the diagram. The large box in the centershows all of the VMs, in this case distributed across two <strong>Dell</strong><strong>Power</strong>Edge 2650 servers—each with dual Intel Xeon processors,8 GB of memory, six physical network interfaces, and 138 GB ofhard disk space—running VMware ESX Server 2.0.1 software.The virtual IP subnets contained various VMs that are depictedin Figure 2 as stars, triangles, and rectangles. Six of the eight subnets(1.1.30.* through 1.1.80.*) were connected to both virtual andphysical systems. The routers, represented by circles between thevirtual subnets, were implemented as VMs running the Linux OSconfigured as a software router. Although not as fast as the hardwareequivalent, a software router—regardless of the implementation,virtual or physical—offers an important benefit: control overthe latency of network communication. This software router configurabilityplayed an important role in simulating the communicationlatencies found in LAN and WAN environments.Evaluating the virtualized Active Directory test environmentThe test plan required that engineers simulate an Active Directorydomain (including subdomains) with up to 25 users. Figure 3presents the relevant information for evaluating the impact ofvirtualization in creating the Active Directory test environment.Comparing an all-physical setup with the hybrid physical-virtualsetup used in this test environment shows that virtualization canhelp reduce deployment efforts and associated costs, and simplifychanging test configurations. 11 For more information, see “Introducing VMware ESX Server, VirtualCenter, and VMotion on <strong>Dell</strong> <strong>Power</strong>Edge Servers” by Dave Jaffe, Ph.D.; Todd Muirhead; and Felipe Payet in <strong>Dell</strong> <strong>Power</strong> <strong>Solutions</strong>, March 2004.24POWER SOLUTIONS June 2004
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