Most, if not all applications, require a durable data store. Although many applications use a relational database engine for durable storage, many others write content directly to a file system. Windows Azure Drives are an infrastructure solution that provides a durable NTFS volume within Windows Azure, thus enabling users to move their data to the cloud and bring it back to their local infrastructure as needed.
When you move to a cloud-based solution, one of the challenges is taking existing Windows applications and running them in the cloud while making sure their data is durable and using the standard Windows NTFS APIs. If you use a Windows Azure drive, your Windows Azure applications running in the cloud can use existing NTFS APIs to access a durable drive. This can significantly ease the migration of existing Windows applications to the cloud. The Windows Azure application can read from or write to a drive letter (for example, X:\) that represents a durable NTFS volume for storing and accessing data.
The durable drive is implemented as a Windows Azure page blob that contains an NTFS-formatted virtual hard disk (VHD). An additional benefit of this approach is that the VHD can be downloaded from the blob store at any time, thus providing customers easy access to their data.
For more information about Windows Azure drives, see the Windows Azure Drive whitepaper.