The following table lists the requirements for the network and the directory servers in your Exchange 2010 organization.

The use of 64-bit Active Directory domain controllers increases directory service performance. In previous versions of Exchange, we recommended a 4:1 ratio of Exchange processors to global catalog server processors, assuming that the processors are of similar models and speeds. This recommendation still applies in Exchange 2010.

 Installing Exchange 2010 on Directory Servers

For security and performance reasons, we recommend that you install Exchange 2010 only on member servers and not on Active Directory directory servers. However, you can't run DCPromo on a computer running Exchange 2010. After Exchange 2010 is installed, changing its role from a member server to a directory server, or vice versa, isn't supported.

The following table lists the scenarios in which coexistence between Exchange 2010 and earlier versions of Exchange are supported.

Coexistence of Exchange 2010 and earlier versions of Exchange Server

 Exchange 2000

You can't upgrade an existing Exchange 2000 organization directly to Exchange 2010. You must first upgrade the Exchange 2000 organization to either an Exchange 2003 or Exchange 2007 organization, and then you can upgrade the Exchange 2003 or Exchange 2007 organization to Exchange 2010. We recommend that you upgrade your organization from Exchange 2000 to Exchange 2003, and then upgrade from Exchange 2003 to Exchange 2010. For more information about upgrading from Exchange 2000, see Planning an Upgrade from Exchange 2000 and Upgrading to Exchange 2007.

The recommended hardware requirements for Exchange 2010 servers vary depending on a number of factors including the server roles that are installed and the anticipated load that will be placed on the servers. For information about minimum, maximum, and recommended hardware configurations for Exchange 2010 servers, see Performance and Scalability.

For more information about planning your hardware for Exchange 2010, see the following topics:

• Understanding Processor Configurations and Exchange Performance
  
• Understanding Memory Configurations and Exchange Performance
  
• Understanding Server Role Ratios and Exchange Performance
  

The following table lists the supported operating systems for Exchange 2010.

Important:

Exchange 2010 RTM doesn’t support being run on computers with the Federal Information Processing Standard (FIPS) compliant settings enabled. If your Windows Server 2008 SP2 or Windows Server 2008 R2 has FIPS enabled, Exchange 2010 RTM will not function correctly. For more information, see The effects of enabling the "System cryptography: Use FIPS compliant algorithms for encryption, hashing, and signing" security setting in Windows XP and in later versions of Windows.

Microsoft supports Exchange 2010 in production on hardware virtualization software only when all the following conditions are true:

• The hardware virtualization software is running:
  
  • Windows Server 2008 with Hyper-V technology
    
  • Windows Server 2008 R2 with Hyper-V technology
    
  • Microsoft Hyper-V Server 2008
    
  • Microsoft Hyper-V Server 2008 R2
    
  • Any third-party hypervisor that has been validated under the Windows Server Virtualization Validation Program.
    
• The Exchange guest virtual machine:
  
  • Is running Microsoft Exchange 2010.
    
  • Is deployed on the Windows Server 2008 with SP2 or Windows Server 2008 R2 operating system.
    
  • Doesn't have the Unified Messaging server role installed. All Exchange 2010 server roles, except for the Unified Messaging server role, are supported in a virtualization environment. This is due to the real-time response requirements associated with voice communications with the Unified Messaging server role.
    
  • Meets all of the requirements set forth previously in this topic.
    
• The storage used by the Exchange guest machine can be virtual storage of a fixed size (for example, fixed virtual hard disks (VHDs) in a Hyper-V environment), SCSI pass-through storage, or Internet SCSI (iSCSI) storage. Pass-through storage is storage that's configured at the host level and dedicated to one guest machine. Pass-through volumes must be presented as block-level storage to the hardware virtualization software, because Exchange 2010 doesn't support using network attached storage (NAS) volumes. The following virtual disk requirements apply:
  
  • Virtual disks that dynamically expand aren't supported by Exchange.
    
  • Virtual disks that use differencing or delta mechanisms (such as Hyper-V's differencing VHDs or snapshots) aren't supported.
    

  Note:
  In a Hyper-V environment, each fixed VHD must be less than 2,040 GB. For supported third-party hypervisors, check with the manufacturer to see if any disk size limitations exist.

• Only management software (for example, antivirus software, backup software, or virtual machine management software) can be deployed on the physical root machine. No other server-based applications (for example, Exchange, SQL Server, Active Directory, or SAP) should be installed on the root machine. The root machine should be dedicated to running guest virtual machines.
  
• Microsoft doesn't support combining Exchange high availability solutions (database availability groups (DAGs)) with hypervisor-based clustering, high availability, or migration solutions. DAGs are supported in hardware virtualization environments provided that the virtualization environment doesn't employ clustered root servers.
  
• Some hypervisors include features for taking snapshots of virtual machines. Virtual machine snapshots capture the state of a virtual machine while it's running. This feature enables you to take multiple snapshots of a virtual machine and then revert the virtual machine to any of the previous states by applying a snapshot to the virtual machine. However, virtual machine snapshots aren't application aware, and using them can have unintended and unexpected consequences for a server application that maintains state data, such as Exchange. As a result, making virtual machine snapshots of an Exchange guest virtual machine isn't supported.
  
• Many hardware virtualization products allow you to specify the number of virtual processors that should be allocated to each guest virtual machine. The virtual processors located in the guest virtual machine share a fixed number of logical processors in the physical system. Exchange supports a virtual processor-to-logical processor ratio no greater than 2:1. For example, a dual processor system using quad core processors contains a total of 8 logical processors in the host system. On a system with this configuration, don't allocate more than a total of 16 virtual processors to all guest virtual machines combined.
  
• When calculating the total number of virtual processors required by the root machine, you must also account for both I/O and operating system requirements. In most cases, the equivalent number of virtual processors required in the root operating system for a system hosting Exchange virtual machines is 2. This value should be used as a baseline for the root operating system virtual processor when calculating the overall ratio of physical cores to virtual processors. If performance monitoring of the root operating system indicates you're consuming more processor utilization than the equivalent of 2 processors, you should reduce the count of virtual processors assigned to guest virtual machines accordingly and verify that the overall virtual processor-to-physical core ratio is no greater than 2:1.
  
• The operating system for an Exchange guest machine must use a fixed sized disk that has a minimum size equal to 15 GB plus the size of the virtual memory that's allocated to the guest machine. This requirement is necessary to account for the operating system and paging file disk requirements. For example, if the guest machine is allocated 16 GB of memory, the minimum disk space needed for the guest operating system disk is 31 GB.
  In addition, it's possible that guest virtual machines may be prevented from directly communicating with fibre channel or SCSI host bus adapters (HBAs) installed in the root machine. In this event, you must configure the adapters in the root machine's operating system and present the LUNs to guest virtual machines as either a virtual disk of fixed size or a pass-through disk.
  

 Root Machine Storage Requirements

Each root machine has minimum disk space requirements that must be met:

• Root machines in some hardware virtualization applications may require storage space for an operating system and its components. For example, when running Windows Server 2008 with Hyper-V, you will need a minimum of 10 GB to meet the Windows Server 2008 System Requirements for the operating system. Additional storage space will also be required to support the operating system's paging file, management software, and crash recovery (dump) files.
  
• Some hypervisors maintain files on the root machine that are unique to each guest virtual machine. For example, in a Hyper-V environment, a temporary memory storage file (BIN file) is created and maintained for each guest machine. The size of each BIN file is equal to the amount of memory allocated to the guest machine. In addition, other files may also be created and maintained on the host machine for each guest machine.
  

 Exchange Server Storage Requirements

The following are the requirements for storage connected to a virtualized Exchange server:

• Each Exchange guest machine must be allocated sufficient storage space on the root machine for the fixed disk that contains the guest's operating system, any temporary memory storage files in use, and related virtual machine files that are hosted on the host machine. In addition, for each Exchange guest machine, you must also allocate sufficient storage for the message queues on the Hub Transport and Edge Transport servers and sufficient storage for the databases and log files on Mailbox servers.
  
• Storage used by Exchange should be hosted in disk spindles that are separate from the storage that's hosting the guest virtual machine's operating system.
  
• Configuring iSCSI storage to use an iSCSI initiator inside an Exchange guest virtual machine is supported. However, there will be reduced performance in this configuration because the network stack inside a virtual machine isn't as full-featured as a non-virtualized network stack (for example, a virtual network stack doesn't support jumbo frames).