openstack 虚拟机迁移时应注意的问题

def migrate_disk_and_power_off(self, context, instance, dest,                                   instance_type, network_info,                                   block_device_info=None):        LOG.debug(_("Starting migrate_disk_and_power_off"),                   instance=instance)        disk_info_text = self.get_instance_disk_info(instance['name'])        disk_info = jsonutils.loads(disk_info_text)
self.power_off(instance)
block_device_mapping = driver.block_device_info_get_mapping(            block_device_info)        for vol in block_device_mapping:            connection_info = vol['connection_info']            mount_device = vol['mount_device'].rpartition("/")[2]            self.volume_driver_method('disconnect_volume',                                      connection_info,                                      mount_device)
# copy disks to destination        # rename instance dir to +_resize at first for using        # shared storage for instance dir (eg. NFS).        same_host = (dest == self.get_host_ip_addr())        inst_base = libvirt_utils.get_instance_path(instance)        inst_base_resize = inst_base + "_resize"        try:            utils.execute('mv', inst_base, inst_base_resize)            if same_host:                dest = None                utils.execute('mkdir', '-p', inst_base)            else:                utils.execute('ssh', dest, 'mkdir', '-p', inst_base) //需确保各主机之间可以无密码登陆            for info in disk_info:                # assume inst_base == dirname(info['path'])