'Notify the backend that it\'s unfrozen/thawed.
This is a gate. We do not allow the backend to be thawed if
it is still failed over.
:param context: security context
:response: True on success
:raises Invalid: if it cannot be thawed.'

def thaw_backend(self, context):

    if self.failed_over:
        msg = _('The    Dell    SC    array    does    not    support    thawing    a    failed    over    replication.    Please    migrate    volumes    to    an    operational    back-end    or    resolve    primary    system    issues    and    fail    back    to    reenable    full    functionality.')
        LOG.error(msg)
        raise exception.Invalid(reason=msg)
    return True
