Exchange Writers for Volume Shadow Copy Service Evaluation Criteria

Application Domain

Applications use VSS to back up and restore Exchange 2003 and Exchange 2007 storage groups, and Exchange 2010 databases. Exchange 2010 and later does not have 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 multiple simultaneously-executing threads to access the VSS COM objects.

Applications typically also use the CHKSGFILES API to verify the database snapshots before writing them to the backup media. The CHKSGFILES APIs can be used in multi-threaded applications, as described in the Exchange Server 2010 Backup and Restore SDK.

Application Architectures

Backup and Restore applications that use VSS to back up Exchange 2010 and later databases 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 to backup Exchange 2010 and later servers must run on the Windows Server 2008 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 2008.

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 2010 writers are installed when Exchange 2010 and later is installed on Windows Server 2008 or later.

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

The Windows VSS APIs can be used in a managed-code environment via a COM Interop Assembly.

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 VSS API and Exchange writers, programmers with experience creating high-reliability software are preferred.

Available Information

For information about VSS, see the Exchange Server 2010 SP1 Backup and Restore SDK and the Windows Development Web site.

Developer / Deployment Licensing

Refer to your Exchange and MSDN subscription licensing agreements to determine whether additional licenses are required for the Exchange 2010 servers that store the data backed up and restored by custom applications that use VSS.

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, and to make requests via the Exchange VSS writers.

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 of the Exchange VSS writers.

Server Platform Requirements

The Exchange 2010 VSS writers are only available when Exchange Server 2010 or later is running on Windows Server 2008 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.