docs: def get_physical_drives(self):
          """Get all the RAID physical drives on the Server.
  
          This method returns all the physical drives on the server
          by examining all the controllers.
  
          :returns: a list of PhysicalDrive objects.
          """
          physical_drives = []
          for controller in self.controllers:
              # First add unassigned physical drives.
              for physical_drive in controller.unassigned_physical_drives:
                  physical_drives.append(physical_drive)
              # Now add physical drives part of RAID arrays.
              for array in controller.raid_arrays:
                  for physical_drive in array.physical_drives:
                      physical_drives.append(physical_drive)
  
          return physical_drives