If sector 0x2106 on the first physical drive houses the RAID superblock, and that sector becomes unreadable, the controller cannot identify the RAID layout. It responds with "Disk Storage Server is Down" because it literally doesn’t know which disks belong to it. Solution: Force a metadata scan from the controller BIOS (Ctrl+R or Ctrl+H during boot).

Most RAID controllers support storcli (Broadcom) or omreport (Dell). Run a weekly: