Volume Shadow Copy Service (VSS)
Forefront TMG uses the Volume Shadow Copy Service (VSS) that is included in the Microsoft Windows Server 2008 operating system to take volume shadow copies of Forefront TMG configuration. Applications that manage backup and restore functionality can manage these functions in Forefront TMG because of the Forefront TMG implementation of VSS. These applications ease the management of backup and restoration for administrators who work with several different applications.
This document provides basic information about the Forefront TMG use of VSS and is intended for developers who want to include Forefront TMG in their backup and restore applications.
VSS is a set of Component Object Model (COM) application programming interfaces (APIs) that provides standardized interfaces, enabling third-party backup and restoration software to centrally manage the backup and restore operations on a variety of applications. VSS also implements a framework that enables volume backups to be performed while applications on a system continue to write to the volumes.
VSS has three components:
Requestor—The application that requests the creation of a shadow copy.
Provider—The interface that provides the functionality to actually make the shadow copy.
Writer—Application-specific software that acts to ensure that application data is ready for shadow copy creation.
Requestors, providers, and writers communicate in the VSS framework to create and restore volume shadow copies. A shadow copy of a volume duplicates all the data held on that volume at one well-defined instant in time.
A requestor initiates the backup and restore processes. The provider controls the processes and instructs a writer to prepare a dataset for backup. When everything is ready, a requestor then instructs a provider to create a shadow copy.
Windows Longhorn Server includes a software-based provider and a general file system writer. The Backup program can communicate with these default VSS components to perform general file system shadow copy backups.
In Forefront TMG, the configuration is stored on the Configuration Storage server, which is an instance of Active Directory Application Mode (ADAM). The Forefront TMG VSS writer makes use of the ADAM VSS writer, and therefore functions only on the Configuration Storage server.
Restoration of a Forefront TMG configuration makes use of the ADAM backup that stores the configuration. Again, this functionality is delegated to the ADAM VSS writer.