@hannu_ikonen@raphaelmorgan second this; any size is probably fine, but a magnetic-platter based device (aka hard disk drive / hdd) is likely the best for TBs worth. Could get a dock and buy bare drives that you store in a cool, dark place, in static bags, too, though it's not necessarily cheaper.
For true archival storage, you can get archival-class dvd/bluray discs that purportedly last 100 years. Because they're write-once, there's no chance of the data degrading, only the chemicals used to make the disc -- which is what sets archival-class apart from non.