What is Microsoft VSS

Microsoft Volume Shadow Copy Service (Microsoft VSS), is a Microsoft Windows Server feature that takes backup snapshots of storage volumes. The snapshots, which can be taken manually or automatically, may be used for restoring logical unit numbers (LUNs) and individual files.

There are several methods by which Volume Shadow Copy Service can make copies. The first is a complete copy, which creates a read-only copy of the original volume. The second method is copy-on-write, which copies only the changes to a volume after a given point in time. It can also make a redirect-on-write copy, which creates a differential copy similar to that of the copy-on-write method, but redirects the changes to a different volume.

VSS allows application data to be backed up while the applications are still running. The feature can be managed as a hardware provider or software provider. A hardware provider manages shadow copies in conjunction with a hardware storage controller and the software provider intercepts input/output requests between the file system and volume manager.

Microsoft VSS was first introduced in Windows Server 2003 and is compatible with NTFS, the file system that the Windows NT operating system uses for storing and retrieving files on a hard disk.