P: Image source on external drive

When I return from the field, I am looking at folders with 3,000 images. If the images are on an external drive, particularly a  slow one, it can take forever for the previews to be rendered. How about an option to save all the previews for a particular folder and/or invoke building previews for a given folder? That way I could have coffee while all the previews are rendering from the external drive and return to work the set uninterrupted.