'Creates LUN on the Unity system.
:param name: lun name
:param size: lun size in GiB
:param pool: UnityPool object represent to pool to place the lun
:param description: lun description
:param io_limit_policy: io limit on the LUN
:return: UnityLun object'

def create_lun(self, name, size, pool, description=None, io_limit_policy=None):

    try:
        lun = pool.create_lun(lun_name=name, size_gb=size, description=description, io_limit_policy=io_limit_policy)
    except storops_ex.UnityLunNameInUseError:
        LOG.debug('LUN    %s    already    exists.    Return    the    existing    one.', name)
        lun = self.system.get_lun(name=name)
    return lun
