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Remote VSS concepts

You should be aware of certain concepts that are required to understand how Remote VSS (Volume Shadow Copy Service) is used by backup services with Hyper-V over SMB configurations.

VSS (Volume Shadow Copy Service)
A Microsoft technology that is used to take backup copies or snapshots of data on a specific volume at a specific point in time. VSS coordinates among data servers, backup applications, and storage management software to support the creation and management of consistent backups.
Remote VSS (Remote Volume Shadow Copy Service)
A Microsoft technology that is used to take share-based backup copies of data that is in a data-consistent state at a specific point in time where the data is accessed over SMB 3.0 shares. Also known as Volume Shadow Copy Service.
Shadow copy
A duplicate set of data contained in the share at a well-defined instant in time. Shadow copies are used to create consistent point-in-time backups of data while the system or applications can continue updating data on the original volumes.
Shadow copy set
A collection of one or more shadow copies, with each shadow copy corresponding to one share. The shadow copies within a shadow copy set represent all the shares to back up in the same operation. The VSS client on the VSS-enabled application identifies which shadow copies to include in the set.
Shadow copy set auto-recovery
The part of the backup process for remote VSS-enabled backup applications where the replica directory containing the shadow copies is made point-in-time consistent. At the start of the backup, the VSS client on the application triggers the application to take software checkpoints on the data scheduled for backup (the virtual machine files in the case of Hyper-V). The VSS client then allows the applications to continue. After the shadow copy set is created, Remote VSS makes the shadow copy set writeable and exposes the writeable copy to the applications. The application prepares the shadow copy set for backup by performing an automatic recovery using the software checkpoint taken earlier. Automatic recovery brings the shadow copies into a consistent state by unrolling the changes made to the files and directories since the checkpoint was created. Automatic recovery is an optional step for VSS-enabled backups.
Shadow copy ID
A GUID that uniquely identifies a shadow copy.
Shadow copy set ID
A GUID that uniquely identifies a collection of shadow copy IDs to the same server.
SnapManager for Hyper-V
The software that automates and simplifies backup and restore operations for Microsoft Windows Server 2012 Hyper-V. SnapManager for Hyper-V uses Remote VSS with auto-recovery to back up Hyper-V files over SMB shares.