Microsoft Knowledge Base Article 822896 contains the following summary:
The Volume Shadow Copy service feature in Microsoft Windows Server 2003 can be used to create applications that back up and restore Microsoft Exchange Server 2003. The Windows Volume Shadow Copy Service (VSS) provides an infrastructure that enables third-party storage management programs, business programs, and hardware providers to cooperate in creating and managing shadow copies. Solutions based on this infrastructure can use the shadow copies (or mirrored copies) to backup and restore one or more Exchange Server 2003 databases.
The Volume Shadow Copy service coordinates communication between Requestors (backup applications), Writers (applications in Windows services like Exchange Server 2003, and SQL Server 2000), and Providers (system, software or hardware components that create the shadow copies). To use the Volume Shadow Copy service feature to backup Exchange Server 2003, the backup program must include an Exchange Server 2003 aware Volume Shadow Copy service requestor. Because the backup program that is bundled with Windows Server has no such requestor, organizations must use third-party backup applications.
In order to be compliant with Exchange Server 2003, VSS based backup applications must follow three basic requirements to ensure the integrity and recoverability of shadow copy backups. If these requirements are not followed, Microsoft Product Support Services (PSS) will consider the backup solution to be outside of the Exchange VSS framework and will not be able to troubleshoot backup and restore issues. Customers should verify with their backup vendors that the backup application fulfills the Exchange-compliant requirements listed in this Knowledge Base article. Details of the Exchange VSS requirements are presented in the "More Information" section of this article.
As with any third party solution, the vendor of the backup application is your primary support provider for backup and recovery issues. PSS can help you diagnose or analyze issues with the available database and transaction log file sets. However, Microsoft does not troubleshoot or debug third party products. PSS assistance is limited to advice about how to best continue to recover the available database and transaction log files.
For more information about how VSS based solutions are supported by PSS, click the following article number to view the article in the Microsoft Knowledge Base:
841696 Overview of the Microsoft third-party storage software solutions support policy