Deployment Flexibility in Microsoft Exchange

Whether deploying on-premises, in the cloud, or in a combination of the two, Exchange 2010 helps reduce costs and provides tools to simplify the deployment experience. Exchange 2010 allows you to:

• Drive down the cost of storage by offering additional storage architecture choices in on-premises deployments
  
• Use hardware virtualization to consolidate multiple under-utilized physical servers in on-premises deployments
  
• Simplify deployment with custom instructions for installing or upgrading to Exchange 2010
  
• Perform migrations during normal business hours without taking users offline
  

http://www.microsoft.com/exchange/en-us/technologies-deployment.aspx