docs: def get_essential_properties(self):
          """Get the essential scheduling properties
  
          :returns: a dictionary containing memory size, disk size,
                    number of cpus, cpu arch, port numbers and
                    mac addresses.
          :raises: IloError, on an error from iLO.
          :raises: IloCommandNotSupportedError, if the command is not supported
                   on the server.
          """
          data = self._call_method('get_essential_properties')
          if (data['properties']['local_gb'] == 0):
              cred = self.snmp_credentials
              if cred and cred.get('snmp_inspection'):
                  disksize = snmp.get_local_gb(self.host, cred)
                  if disksize:
                      data['properties']['local_gb'] = disksize
                  else:
                      msg = self._('SNMP inspection failed to '
                                   'get the disk size. Returning '
                                   'local_gb as 0.')
                      LOG.debug(msg)
              else:
                  msg = self._("SNMP credentials were not set and "
                               "RIBCL/Redfish failed to get the disk size. "
                               "Returning local_gb as 0.")
                  LOG.debug(msg)
          return data