Restore of a RAID1 on a R350 with a RS820+

Hello,

we have been using this RS820+ for several years and have already carried out backups and restores. But now we have a problem restoring an R350 from Dell. 
The boot medium can be started and I can also select the backup. However, there are always complaints that the hard drives are too small for the backup. 
However, when I look at which drivers the boot medium loads, no RAID controller (H755 Front SAS) is listed here. Could it be that only the driver for the RAID controller is missing? I had already looked at Dell, but unfortunately I couldn't find a driver (".inf") that I could download. 
Has anyone had a similar experience? Where can I get such a driver?

Best regards,

Stefan