SharePoint VSS Reference Writer
The Volume Shadow Copy Service (VSS), new to Windows Server 2003 and Windows Storage Server 2003, is the infrastructure that provides built-in shadow copy capabilities. Shadow copies created by VSS augment the storage administrator’s tape backup archival solutions, providing high fidelity point-in-time copies that can be created and restored easily and effectively, thereby helping to simplify several aspects of storage and data management. Microsoft Office SharePoint Server 2007 uses VSS to simplify backup and restore operations. Following are the SharePoint VSS solution features and characteristics:
A single VSS reference writer. There has been no easy way for applications to describe their data to backup applications. To successfully back up various Windows platform applications, backup applications have an excessive number of APIs that they need to write specific code for. The SharePoint VSS writer enables backup applications to take advantage of the single writer to backup Office SharePoint Server 2007.
Full farm backup and restore for catastrophe. The writer allows a backup application (requestor) to easily access the VSS API to request a backup or a restore operation for an entire SharePoint farm, including a single box setup or a Web farm configuration.
Database level granularity. The writer allows requestor to select all databases, a segment of the databases (multiple select), or a single database (single select) for both backup and restore operations. All databases, except configuration and Central Administration content database are selectable through the writer. Configuration and Central Administration content database need to be backed up or restored as part of the whole farm.
SharePoint inventory list. Before backup, the SharePoint writer generates a flat inventory list of databases selected for backup within the farm. The list is returned to the requestor so that backup can be run on the location where the database is physically located.
Web farm configuration support. The writer understands and provides support to synch up backup and recovery on a Web farm scenario in a limited way. The writer provides the requestor with a list of inventory of servers, databases, and files associated with the farm. The requestor is responsible for making a separate connection to each server to call the VSS writer on that server to generate the backup or to run the restore operation.
Backup content without interruption. An application can modify a file while it is being backed up, causing data corruption or causing an error when the file is opened. VSS allows a quick snapshot of the application to be made to the shadow copy, while allowing the application to operate at the original location without interruption.
Third-party pluggable database backup and recovery. The writer offers pluggable/extensible backup for third-party solutions built on top of Office SharePoint Server 2007. However, only databases that are registered within the configuration database are included in the writer. Any additional files and unregistered databases are not included.
Search index files backup and recovery. Because search index files are stored in the file system, a separate file writer is needed to them up back up. To resolve this, Office SharePoint Server 2007 includes a separate search writer that handles search index files. To simplify the process for backup application writers, Office SharePoint Server 2007 declares cross-writer dependencies in such a way that search index files are also backed up or restored when backing up registered databases in the farm.
Full SharePoint application rollback. The writer handles all components within a SharePoint application, including databases such as the configuration database, content databases, SSP databases, and Search database. As mentioned previously, the writer also has a dependency on the Search writer, which handles all the Search index files for backup and recovery. At the time of recovery, the writer can roll back the entire SharePoint application by restoring a previous farm backup.
Post-restore synchronization of databases. To ensure that all databases are synchronized with the farm after a restore operation is complete, each of the databases are automatically detached and reattached to the farm post recovery. Administrators do not need to run additional procedures to resynchronize the restored databases.
Functions Performed by the Writer
The writer performs the following functions:
Builds SharePoint components.
Generates a full inventory list of all components within the SharePoint farm.
Is not necessarily tied to backup process or restore process.
Backs up farm or database.
- Requests a SharePoint (farm/database) backup via VSS.
Restores a farm or database.
Requests a SharePoint (farm/database) recovery via VSS.
SharePoint implements postRestore() to synchronize sites table.