Hardware virtualization software lets you run multiple operating system instances at the same time on a single computer. Microsoft has the following two software offerings that provide this functionality:

•	Microsoft Virtual PC
•	Microsoft Virtual Server

Third parties also have software on the market that provides this functionality.

This article describes the Microsoft support policy for Microsoft Exchange Server 2003 running on hardware virtualization software (virtual machines).

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Support policy for Exchange Server 2003

Microsoft supports Exchange Server 2003 running on hardware virtualization software (virtual machines) only when all the following conditions are true:

•	The hardware virtualization operating system is Virtual Server 2005 R2 or a later version.
•	The version of Exchange Server that is running on the virtual machine is Microsoft Exchange Server 2003 Service Pack 2 (SP2) or a later version.
•	The Microsoft Virtual Server 2005 R2 Virtual Machine Additions are installed on the guest operating system.
•	Exchange Server 2003 is configured as a stand-alone server, not as part of a Windows cluster.
•	The SCSI driver that is installed on the guest operating system is the Microsoft Virtual Machine PCI SCSI Controller driver.
•	The virtual hard disk Undo feature is not enabled.

Note When a Microsoft Virtual Server SCSI adaptor is added to a virtual machine after the Virtual Machine Additions have been installed, the guest operating system detects and installs a generic Adaptec SCSI driver. In this case, the Virtual Machine Additions must be removed and then reinstalled for the correct SCSI driver to be installed on the guest operating system.

To verify the SCSI driver that is installed on the guest operating system, follow these steps:

1.	On the guest operating system, click Start, right-click My Computer and then click Manage.
2.	Under System Tools, click Device Manager.
3.	Under SCSI and RAID controllers, verify that Microsoft Virtual Machine PCI SCSI Controller is listed. If you see a different driver, you must reinstall the Virtual Machine Additions. For example, if you see Adaptec listed, you must reinstall the Virtual Machine Additions. Note If the virtual machine is configured to use an IDE controller only, no action is required.

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Performance and scalability considerations

When you plan to deploy Exchange Server 2003 SP2 in a virtualized environment, the same performance and scalability aspects that are described in the "Exchange Server 2003 Performance and Scalability Guide" apply when you size each virtual machine for Exchange Server 2003.

However, there are some factors that directly affect the performance and scalability of Exchange Server 2003 when Exchange Server 2003 is running on Virtual Server 2005 R2. These factors should be considered when you size both the host configurations and the guest configurations.

Virtual machine considerations

•	Each virtual machine can have only one CPU. This limits the processing power of the virtualized Exchange Server 2003 installation. The server should be sized in such a way that a single CPU can handle the estimated load on the server. Also, the number of virtual machines that are running at the same time on the host computer will affect the overall performance of the whole system.
•	When you size the disk capacity of the virtual machine, the time that is required to perform a full online backup of the Exchange Server data over the network should be considered. Consider adding a dedicated virtual network adaptor for Exchange Server backups. Note Although you can perform an offline backup of the virtual hard disk (.vhd) files at the host level, this does not replace the need for performing a regular Exchange Server backup. For more information about Exchange Server backup and restore processes, see the "Exchange Server 2003 Disaster Recovery Operations Guide."
•	Create separate fixed-size virtual disks for Exchange Server databases and log files and store them on separate physical drives on the host server.
•	Exchange Server performance should be validated before production by using the Exchange Server 2003 Performance Tools. For more information about these tools, see the "Exchange Server 2003 Performance and Scalability Guide."

Host considerations

•	Make sure that the server that is running Virtual Server 2005 R2 is sized correctly to handle the number of virtual machines that you plan to deploy. This estimate should include CPU, memory, network adaptors, and disk configuration.
•	Use a hard disk solution that enables fast access. You can use a SCSI hard disk, a redundant array of independent disks (RAID), or storage area network (SAN) to store the .vhd files that are used by Exchange Server data.
•	If an antivirus program is installed on the host, the antivirus program should be configured not to scan .vhd files.

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Support policy for non-Microsoft hardware virtualization software

Microsoft has a general support policy for running Microsoft software in non-Microsoft hardware virtualization software. The policy that is described in the following Microsoft Knowledge Base article also applies to any version of Exchange Server that is running in non-Microsoft hardware virtualization software: For more information about the Microsoft Virtual Server support policy, click the following article number to view the article in the Microsoft Knowledge Base:

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For more information about Virtual Server 2005 R2 performance and scalability, see the "Virtual Server 2005 R2 Administrator’s Guide." To see the "Virtual Server 2005 R2 Administrator’s Guide," visit the following Microsoft Web site:For more information about Exchange Server 2003 performance and scalability, see the "Exchange Server 2003 Performance and Scalability Guide." To see the "Exchange Server 2003 Performance and Scalability Guide," visit the following Microsoft Web site:For more information about Exchange Server backup and restore processes, see the "Exchange Server 2003 Disaster Recovery Operations Guide." To see the "Exchange Server 2003 Disaster Recovery Operations Guide," visit the following Microsoft Web site:

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