Virtual Server 2005 allows users to run multiple independent operating system instances on a single piece of hardware. Virtual Server 2005 runs as a service on Microsoft Windows Server 2003 and provides the framework in which the virtual machines run. Each virtual machine can have its own hard disk drives that correspond to files on the host operating system. In essence, a full backup of a virtual machine would entail backing up the configuration and the hard disk files.
When working with Virtual Server, be aware of the terms guest and host machines. Host machines describe the physical server and the operating system running on that server, whereas guest machines are those virtual server sessions that run on top of the host operating system.
This virtualization has several benefits. First, it allows for greater utilization of hardware resources. Because more than one server can run on a single piece of hardware, hardware can be used more efficiently. Second, because all virtual hardware drivers (such as video, network, and hard disk resources) within a virtual machine are the same, virtual machines can be moved to different hardware running Virtual Server 2005 with minimal effort.
Service-based Virtual Server 2005, unlike Microsoft Virtual PC 2004, runs as a service on the host operating system. This allows for virtual machines to run regardless of desktop interaction and allows them to be started automatically after a host server reboot.
Hardware standard within the virtual machines Regardless of the disk interface, network adapters, or video adapters in the host machine, the virtual machines always see the same types of hardware. This allows for virtual machines to be moved from host server to host server without requiring reconfiguration within the virtual machines.
For a complete list of the hardware that is emulated within the virtual machines, see the Virtual Server 2005 help file.
Multiple network access methods Virtual Server 2005 allows direct access to the network by virtual machines through physical network adapters in the host. In addition, virtual networks can be created that are only visible to one or more virtual machines.
Scriptable interface Virtual Server 2005 provides a scripting interface that can be used to automate creating virtual machine definitions, changing their configuration, and rebooting the virtual machines through scripts. There are also various other capabilities exposed by the scripting interface.
This benefit also opens up a vulnerability, as ISA Server could be shut down by scripting a shutdown of the guest operating system on which it runs, or by attacking the host machine.
Undoable drives Undoable drives provide the ability to make changes to a virtual machine, such as major configuration changes or software updates, and then undo those changes. This can be valuable when testing patches or service packs or when automating software installation packages.
Be vigilant as you use the Undo Disks feature. If it is not used correctly, you could lose changes you want to keep.
There are several situations in which Virtual Server 2005 can be quite beneficial. Although not an exhaustive list, this section provides several examples.
Earlier application support Earlier applications that cannot run under upgraded operating systems might be supported by running them as virtual machines with an earlier operating system, thereby allowing you to replace dated hardware while keeping the earlier operating systems and applications in place.
Migrations During migrations it is often useful to test upgrades in an environment that will not affect production systems. By copying ISA Server computer configurations, along with other key servers, to a virtual machine, it is possible to test upgrades of software and operating systems to ensure compatibility before upgrading the actual production environment.
Because licensing can vary by customer and situation, you should check with your Microsoft licensing representative to ensure that you have the appropriate licenses required for your particular situation.
Test labs Virtual Server is an excellent tool for creating test labs that can be used for training purposes or for validating procedures for maintenance or upgrades. Often, Virtual Server is used as part of a production rollout scheme to mirror an entire production environment without having to mirror all the hardware of the production environment. Updates to application code or software and operating system patches can be installed in the Virtual Server environment first for validation and then rolled out to production.
Demonstrations Virtual Server can be used to demonstrate all types of environments. These can be full-fledged multiserver installations that can run on a laptop and be taken wherever needed.
Disaster recovery A good disaster recovery plan includes the ability to quickly bring up a secondary test site in case of a catastrophe. Virtual Server can be used to provide an off-site platform for running systems after a disaster. This could be configured as either a warm backup from which to restore current data after a disaster or as a hot backup site that is continually updated using replication software with the primary site.
Configuration builds When implementing Virtual Server 2005 in a production environment, an installation of ISA Server 2004 in a virtual machine can be used to create the configurations for the production server. This allows for large changes to be made and verified in a test environment before you roll those changes out to the production ISA server.
Be certain that you verify that you are not violating any licensing agreements by checking with your Microsoft licensing representative, and reading the End User Licensing Agreement (EULA) for each product.
Applications in a box There might be situations in which it is advantageous to have an entire test environment consisting of several servers in a single, portable configuration. For example, you might need to place an entire Web application on a single piece of hardware. This might include an ISA Server 2004 computer, a Web server, a business components server, and a database server packaged and consolidated on a single portable machine.
The guest operating system stores its disks as files on the host operating system—these files are called virtual disks. Virtual disks come in several different types. Table 19-1 shows the different types of disks and the advantages of each type.
Dynamically expanding disks are disk files that grow as needed on the host server. For example, the ISA2004SE virtual machine that you create might have a 16-GB partition; however, it would only use 2 to 3 GB on the host server because there is only 2 to 3 GB of data being used on that partition.
The advantage of dynamically expanding disks is that they only use as much space on the host operating system disk as needed. If you define a 16 GB dynamically expanding virtual disk, the file will only be as large as is needed to store the files in it, and the file will expand as needed. However, performance can suffer when the disk needs to expand. In addition, it's possible for the host server's physical hard disk to run out of space, preventing the dynamically expanding disk from growing.
Fixed size disks preallocate all the space that could potentially be used for a virtual disk. For example, an ISA Server virtual machine created with a 16 GB virtual hard disk would take up 16 GB of space on the host server.
The advantage of fixed size disks is that the space is already allocated, which makes it unlikely that the host server would accidentally run out of space. Furthermore, fixed sized virtual disks can decrease fragmentation on the host system that can be caused by expanding disks—the performance on the guest operating system can increase because the file does not need to expand.
Differencing disks are disks that only record changes from another disk. For example, suppose you have a Windows Server 2003 virtual machine. Once Windows Server 2003 is installed and fully patched and all related software has been loaded, that virtual hard disk can be used as the source for differencing disks. This could allow for several different Windows Server 2003 virtual machines all based on the single source image, while consuming much less disk space than would be required if each virtual machine used its own virtual disk.
These are disks that actually read files directly on the host system's hard disk.
Images can include CD and floppy disk images and are typically in the ISO CD disk format (file extension .iso).
Because virtual disks on a virtual server can compete against each other for disk access resources, fast disk speeds are important for a production Virtual Server 2005 environment. Best disk performance can be achieved by using a separate disk channel from the host, such as a dedicated Small Computer Software Interface (SCSI) hardware array.
The Virtual Server Migration Toolkit is available for simplifying moving physical servers to a virtual server environment. Information can be found at http://www.microsoft.com/windowsserversystem/virtualserver/.