Depends on what you mean by ‘all files and storage’. If what you are moving to the external drive are databases that have all the data imported, then you will be fine. Just close the databases in DEVONthink before the move, then launch the app and open them again. If your databases contain documents that are indexed, then that will be problematic. You cannot move the documents to a different drive (or even a different location on the same drive) and maintain the index link.
User-created databases and their corresponding documents are the only thing I might want on another drive-was there anything else in particular that you were planning on moving off the main drive?