I do not have Dell C6220 , but I do have 5 x Intel quad nodes servers ( almost like the C6220 ).
Wait for Patrick to answer you question because he has Dell C6220 system.
My best guess is that you may need to load the Intel C602 PCH driver.
For my Intel nodes, here is the download link
Drivers & Software
This download provides support for the Intel® C600/C222/C224/C226 Chipsets on onboard SATA or SAS Controller in RSTe mode
I have to load the Intel PCH Drivers for the nodes to see the disks.
Wait for Patrick to answer you question because he has Dell C6220 system.
My best guess is that you may need to load the Intel C602 PCH driver.
For my Intel nodes, here is the download link
Drivers & Software
This download provides support for the Intel® C600/C222/C224/C226 Chipsets on onboard SATA or SAS Controller in RSTe mode
I have to load the Intel PCH Drivers for the nodes to see the disks.