VDC_Snapshot

When BACKUP WITH SNAPSHOT is used, this command indicates that Microsoft® SQL Server™ has suspended writes to its database files. The application must copy the files as quickly as possible and then complete the command. To abort the command, the application should return the 'ERROR_OPERATION_ABORTED' error code. For more information, see SNAPSHOT Support.

At the time this command is received, the meta data that is being written over the VDI channel is complete. The application may close its output stream and is free to include the meta data with the actual data portion of the snapshot.