<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def mount(self, volume):
 """Add the volume to a RAID system. The RAID array is activated as soon as the array can be activated. :raises NoLoopbackAvailableError: if no loopback device was found """


        volume._find_loopback()

        raid_status = None
        try:
            # use mdadm to mount the loopback to a md device
            # incremental and run as soon as available
            output = _util.check_output_(['mdadm', '-IR', volume.loopback], stderr=subprocess.STDOUT)

            match = re.findall(r"attached to ([^ ,]+)", output)
            if match:
                volume._paths['md'] = os.path.realpath(match[0])
                if 'which is already active' in output:
                    logger.info("RAID is already active in other volume, using %s", volume._paths['md'])
                    raid_status = 'active'
                elif 'not enough to start' in output:
                    volume._paths['md'] = volume._paths['md'].replace("/dev/md/", "/dev/md")
                    logger.info("RAID volume added, but not enough to start %s", volume._paths['md'])
                    raid_status = 'waiting'
                else:
                    logger.info("RAID started at {0}".format(volume._paths['md']))
                    raid_status = 'active'
        except Exception as e:
            logger.exception("Failed mounting RAID.")
            volume._free_loopback()
            raise SubsystemError(e)

        # search for the RAID volume
        for v in volume.disk.parser.get_volumes():
            if v._paths.get("md") == volume._paths['md'] and v.volumes:
                logger.debug("Adding existing volume %s to volume %s", v.volumes[0], volume)
                v.volumes[0].info['raid_status'] = raid_status
                volume.volumes.volumes.append(v.volumes[0])
                return v.volumes[0]
        else:
            logger.debug("Creating RAID volume for %s", self)
            container = volume.volumes._make_single_subvolume(flag='alloc', offset=0, size=volume.size)
            container.info['fsdescription'] = 'RAID Volume'
            container.info['raid_status'] = raid_status
            return container