'Return size of volume to be managed by manage_existing.
existing_ref is a dictionary of the form:
{\'source-name\': <name of the virtual volume>}'

def manage_existing_get_size(self, volume, existing_ref):

    target_vol_name = self._get_existing_volume_ref_name(existing_ref)
    if re.match('osv-*|oss-*|vvs-*', target_vol_name):
        reason = _('Reference    must    be    for    an    unmanaged    virtual    volume.')
        raise exception.ManageExistingInvalidReference(existing_ref=target_vol_name, reason=reason)
    try:
        vol = self.client.getVolume(target_vol_name)
    except hpeexceptions.HTTPNotFound:
        err = (_("Virtual    volume    '%s'    doesn't    exist    on    array.") % target_vol_name)
        LOG.error(err)
        raise exception.InvalidInput(reason=err)
    return int(math.ceil((float(vol['sizeMiB']) / units.Ki)))
