Backup or restore operations that use the Microsoft SQL Server Virtual Device Interface (VDI) require that the server connection for SQL Server that is used to issue the BACKUP or RESTORE commands must be logged on as the sysadmin fixed server role. This may not be desirable in all environments and may cause third-party backup applications that use VDI to fail if the service accounts of the applications are configured to only have the db_backupoperator fixed database role. This is a design limitation in the current versions of SQL Server.
The VDI connection requires the Sysadmin permission because the connection itself is capable of executing more than simple backup operations and involves shared resources between the client and server. The Microsoft SQL Server product team is evaluating this requirement for the next major version of SQL server, and this Microsoft Knowledge Base (KB) article will be updated when additional information is available.
For additional information about SQL Server backup and restore operations, consult the following Microsoft TechNet webpage:
BACKUP (Transact-SQL) For additional information about Volume Shadow Copy Service (VSS) and VDI backups in SQL server, consult the following MSDN blog post.
Informational: Shedding light on VSS and VDI backups in SQL Server Application vendors can consult the following guide for additional information about using VSS for SQL server backups.