restore with multiple drives

Hi, I met a problem when resotring.

When I backup object by 4 drives, it cost 5H but when I do restore by more than 2 drives, it will failed with error: "Retore of object eccplla:P11.15 named "SAP", may be incomplete because some media is missing."

If I tried to restore by only one drive, it will successed by cost 50H, may I know whats happened and what I can do to save the restore time?

Thank you!