To improve performance, raw-volume backup is suitable.
But you can only backup and restore whole data in volume without option product. FlashBackup(shipped in Advanced Client option) enable you to restore individual file in volume.
Check NetBackup Advanced Client System Administrator's Guide(for 5.x) or NetBackup FlashBackup System Administrator's Guide (for 4.5, but easier to understand overview).
VERITAS NetBackup 5.1 Advanced Client System Administrators Guide for UNIX and Windows
http://support.veritas.com/docs/268106
NetBackup FlashBackup 4.5 System Administrator's Guide for UNIX
http://support.veritas.com/docs/246818