A RAID Redundant Array of Independent Disks (Redundant Array of Independent Disks) is a data storage scheme using multiple hard drives to share or replicate data among the drives. To ensure that the RAID system is detected and properly displayed on the Dashboard, you need to use a RAID controller that is supported by Sophos UTM. Check the HCL Hardware Compatibility List to figure out which RAID controllers are supported. The HCL is available at the Sophos Knowledge Base. Use "HCL" as search term to locate the corresponding page.
Sophos UTM Administration Guide