Exchange Writer for VSS Evaluation Criteria

Topic Last Modified: 2008-08-07

The Volume Shadow Copy Service (VSS) component of the Windows Server 2003 and later operating systems coordinates the activities of providers, writers, and requestors for creating and using shadow copies. The VSS writer for Microsoft Exchange Server 2007 enables applications to back up and restore Exchange storage groups that are stored on hardware that supports the VSS.

Caveats

Backups using the Volume Shadow Copy service are performed at only the storage group level. Individual databases cannot be backed up. Restoring an individual database from a Volume Shadow Copy Service backup is supported; however, the entire storage group must be offline during the restore. Although multiple Exchange storage groups can be backed up at a time using the Volume Shadow Copy Service, only one backup can be performed at a time.

Functional Criteria

Criteria	Exchange Backup and Restore API
Application Domain	Applications use VSS to back up and restore Exchange 2003 and Exchange 2007 storage groups.
Major Objects	Applications that use the VSS to back up and restore whole storage volumes use COM objects and interfaces that include the following: IVssAsync, IVSSBackupComponents, IVssComponent, IVssCreateWriterMetadata, IVssEnumObject, IVssExamineWriterMetadata, IVssWMComponent, IVssWMDependency, IVssWMFiledesc, IVssWriterComponents, IVssWriterComponentsExt.
Data access model	Access to data inside a VSS shadow copy depends on the hardware vendor's implementation. Exchange should not be used to directly access the storage group data inside the shadow copy. The data must be restored to its original location before Exchange can mount the storage group.
Threading Models	Single threading only. When an application uses VSS and the Exchange writer to back up or restore data, the code that accesses VSS and the Writer should be single-threaded. Applications should not use a multiple threads to access the VSS COM objects.
Application Architectures	Backup and Restore applications that use VSS to back up Exchange 2003 storage groups typically consist of a background service that performs the backup, a scheduling service, and a Windows GUI application console that controls and configures the backup and restore system.
Remote Usage	Applications that use VSS must run on the Windows Server 2003 computer on which the Exchange store process is running. Because of the flexibility in large storage systems, the hardware hosting the storage volumes might not actually be a physical part of the computer running Windows Server 2003.
Transactions	No.
Management Capabilities	Applications that use VSS can take advantage of the Windows Events and performance counters provided by VSS, the Exchange writer, and any that are provided by the VSS-compatible storage hardware vendor.
Availability	VSS is a component of Windows Server 2003 and later versions of the operating system. The Exchange writer is installed when Exchange 2003 or Exchange 2007 is installed on Windows Server 2003 or later.

Development Criteria

Criteria	Exchange Backup and Restore API
Languages and Tools	VSS can be used in any COM-compatible language. It is most frequently used in applications written in C++. Because creating shadow copies requires the Exchange store to be momentarily taken offline, backup applications are typically very time-sensitive, which in most cases prevents using languages like Visual Basic or VBScript.
Managed Implementation	VSS cannot be used in a managed-code environment.
Scriptable	Yes, but not recommended.
Test/Debug Tools	No special tools are required to debug applications that use the Windows Volume Shadow Copy Service.
Expert Availability	Finding developers who can effectively program VSS applications should not be difficult. Although relatively few developers have used VSS previously, the level of information and support from hardware vendors and Microsoft should enable most programmers to work with VSS. Because of the nature of the Backup and Restore API, programmers with experience creating high-reliability software are preferred.
Available Information	For information about VSS, see the Exchange Server 2007 SDK and the Windows Deve l opment Web site.
Developer / Deployment Licensing	Refer to your Exchange and MSDN subscription licensing agreements to determine whether additional licenses are required for the Exchange 2007 servers that store the data backed up and restored by custom applications that use VSS.

Security Criteria

Criteria	Exchange Backup and Restore API
Design-Time Permissions	The VSS infrastructure requires VSS requestors, such as backup applications, to be able to function both as COM clients and as a server. Requestors need to securely manage which COM clients are able to make incoming COM calls into its process. The requestor-specific security settings must allow outgoing COM calls from the requestor to the VSS service and writer processes.
Setup Permissions	No special permissions are required to install applications that use VSS. Because the applications must run on the computer running Exchange, the account under which the application is installed must have sufficient permission to install software on that computer.
Run-Time Permissions	A VSS requestor typically needs to be run under an account that is either a member of the Administrators built-in group or the Backup Operators group.
Built-in Security Features	VSS requestor applications can use CoInitializeSecurity to set a process-wide permission check of default COM access. VSS writers can also be set to allow all process access to call into the requestor processes or set to allow only specific processes access to call into the requestor process. Additional registry settings can be configured to allow access to specific applications.
Security Monitoring Features	There are no built-in security monitoring features.

Deployment Criteria

Criteria	Exchange Backup and Restore API
Server Platform Requirements	VSS is only available when Exchange Server 2003 or Exchange 2007 is running on Windows Server 2003 or later.
Client Platform Requirements	There are no special client requirements beyond the VSS core requirements.
Deployment Methods	VSS applications can be installed on servers by using standard software distribution technologies.
Deployment Notes	None.