Microsoft SQL Server Virtual Backup Device Specification
VDF_WriteMedia (0x10000)
This bit is set by Microsoft® SQL Server™. Only this and the VDF_ReadMedia feature bit are set in this manner. It is visible after IClientVirtualDeviceSet2::GetConfiguration returns the final configuration. This bit is for the convenience of the client, informing it that a BACKUP is being performed and that it should be prepared to receive VDC_Write data transfer commands.