The backup process of my hard drive in my laptop takes a very long time which I haven't measured and can't estimate. Sometimes I would like to suspend the backup process, so that I can suspend my OS Ubuntu and bring it to some other place by taking a bus, or I can do something else under Ubuntu without being bothered by the backup process. 

Can I suspend a backup process by rsync, then umount and unplug the backup storage device, then reattach and mount the device, and finally resume the backup process by rsync?

Will the resumed process by rsync work, except that it doesn't back up any change made during the detached period to the files already backed up?

Is restarting rsync command after reattach and mount the external storage device, the only solution?

Thanks.