Backup job very very slow and diver show idle

NBU 6.5.2A( I know too old :( )

Windows 2003 R2 SP2

Everything was ok until the tape library was fixed after hard crash.

I use HP storageworks tool to test drive and work well. But do the backup job via NBU it is very very slow( 1 file 3.5GB 5hours).

When the job was running, the tape library screen show " driver idle" .

Any advices except upgrade? 

Best regards.