Relation between SQL Server 2005 and Volume Shadow Copy services?
Until last month I was not aware about Volume Shadow Copy and what is the relation between that service & SQL Server services, so here I would like to give the information in this regard that will discuss SQL Server connection issues that you may encounter when you use Volume Shadow Copy Service (VSS) enabled backup applications.
SQL Server 2005 provides support for Volume Shadow Copy Service (VSS) by providing a writer (the SQL writer) so that a third-party backup application can use the VSS framework to back up database files. This paper describes the SQL writer component and its role in the VSS snapshot creation and restore process for SQL Server databases. It also captures details on how to configure and use the SQL writer to work with backup applications in the VSS framework.
The SQL Writer Service provides added functionality for backup and restore of SQL Server 2005 through the Volume Shadow Copy Service framework. I think from Windows Server 2003 operating system & SQL Server 2005 installation onwards this SQL Writer Service is automatically installed but not enabled by default. It must be explicitly enabled to run on the server machine and must be running at the time that the Volume Shadow Copy Service (VSS) application requests a backup or restore. I believe this has changed and since SQL Server 2005 Service Pack 2 it configures SQL Writer to start automatically
To dig further I have been browsing through the Technet/MSDN articles that refers :
The VSS is a set of COM APIs that implements a framework to allow volume backups to be performed while applications on a system continue to write to the volumes. The VSS provides a consistent interface that allows coordination between user applications that update data on disk (writers) and those that back up applications (requestors).
The VSS captures and copies stable images for backup on running systems, particularly servers, without unduly degrading the performance and stability of the services they provide. For more information on the VSS, see your Windows documentation.
A VSS writer (MSDE Writer) shipped with the VSS framework in Microsoft Windows XP and Microsoft Windows Server 2003. This writer coordinates with SQL Server 2000 and earlier versions to help in backup operations. With SQL Server 2005 installation, SQL Writer is the preferred writer, though MSDE Writer will continue to work and will be the default writer if installed and SQL Writer is not enabled. To start and use the SQL Writer, first disable the MSDE writer from enumerating SQL Server 2005 databases.
SQL Writer service must run under the Local System account.
Further study reference on SQL Writer and VSS refer to SQLWriter article and VSSBASics blog links.