Volume Shadow Copy Service (VSS) is a Windows service that provides the capability of creating snapshots or volume shadow copies. A volume shadow copy is a volume that represents a duplicate of the state of the original volume at the time the copy began. Thus, through VSS, point-in-time copies of data can be saved and used for different purposes, such as backup or application testing.

VSS snapshots represent an advance in snapshot technology because snapshots can be taken when application files are open. VSS interacts with an application (such as Microsoft SQL Server) and can quiesce the application for the moment when the snapshot is created. VSS restarts the application immediately after the snapshot. VSS only takes snapshots of read or write volumes and the resulting volume shadow copy is a read-only volume.