Application Compatibility: Volume Shadow Copy Service

Brief Description

Volume Shadow Copy Service (VSS) is a new service that was introduced in Windows XP® and Windows Server® 2003. It is a framework facilitating communication between applications, storage subsystems, and storage management applications (including backup applications). This service defines, persists, and exploits point-in-time copies of storage data.


Compatibility with Windows XP Backup Applications

Several interfaces have changed since Windows XP, and the libraries are not compatible with Windows Vista® and Windows Server® 2008. At a minimum, the application will need to be recompiled using either headers or libraries from VSS SDK 7.2 or from the Platform SDK released with Windows Vista and Windows Server 2008.

Compatibility with Windows Server 2003 SP1 Backup Applications

Binaries from Windows Server 2003 Service Pack 1 (SP1) are compatible with Windows Vista and Windows Server 2008. Most backup applications would also need to account for the changes in the inbox writers, file and registry virtualization, and WRP as well as the use of hard links in %windir%system32. These differences makes it unlikely that a backup application from Windows Server 2003 SP1 will work as-is.

Compiling Backup Applications for Windows Vista and Windows Server 2008

Applications that use interfaces available in Windows Server 2003 can be compiled using the headers and libraries provided in VSS SDK 7.2. To use new interfaces specific to Windows Vista and Windows Server 2008, recompile using the VSS headers and libraries included in the Platform SDK for Windows Vista and Windows Server 2008.

VSS Writers

Registry Writer

The Registry Writer now performs in-place backups and restores of the registry as compared to the earlier spit writer scheme. User hives are not reported by the Registry Writer.

COM+ RegDB Writer

This writer backs up the contents of  %systemroot%\registration. COM+ depends on a registry key being backed up and therefore needs to be backed up and restored with the registry.

MS Search Writer

This writer deletes the search index from shadow copies after creation.

MSDE Writer

This writer is the default writer for SQL 2000 and SQL 2005 databases.

WMI Writer

This writer is used for backing up WMI-specific states and data during backup operations. The data includes files from the WBEM Repository and requires registry backup.

Background Intelligent Transfer Service (BITS) Writer

This writer uses the FilesNotToBackup reg key to exclude files from the directory %allusersprofile%\application\data\microsoft\network\downloader.

Automated System Recovery (ASR) Writer

This writer stores the configuration of the disks on the system.

System Writer

Under Windows Vista and Windows Server 2008, this writer will generate a list of files using the following formula:

  1. All static files that have been installed. These files are identified by the attribute writeabletype = "static" or "" (empty string) in the component manifest. This category will include all WRP files; additionally, there might be some files marked as static that are not WRP. For example, games are static but not WRP so that administrators can change parental controls.

  2. The WinSxS folder, which includes all manifests, optional components and 3rd party Win32 files.

  3. All PnP Files for installed drivers (owned by PnP).

  4. All user-mode services and non-PNP drivers.

  5. All catalogs owned by the CryptSvc service.

The files in %windir%\system32 are hard links to the winsxs directory.

The restore application is responsible for laying down files and registry and setting access control lists (ACLs) to match the system snapshot. The appropriate hard links must also be created.

Microsoft Optimization Writer

This writer deletes certain files from the snapshots. The file deletions are done to minimize Copy On Write (COW) I/O during the snapshot maintenance phase, and the files are typically temporary files or those that do not constitute user or system state.

Links to Other Resources

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