Without question, the best data storage device of all time is pencil and paper. Why? Because physically it lasts for millenia; it's not device-dependent; the information is written in languages that are stable over periods of centuries -- and there are zero supply constraints on the media!
Really, this is no joke. How many worthwhile things were recorded ONLY on old floppies that can no longer be read? (Even if there were a drive to read them on, those things were notorious for losing their physical integrity and formatting over a span of only a few years; by now their contents are hash.) Optical media are an improvement, but their archival performance is an open question -- especially for rewritable media, which are after all designed NOT to be archival.
Some of the oldest documents known are on paper. It deteriorates physically unless it's well made and stored under good conditions, but we're still talking centuries here. Even a garden-variety xerox copy will be around for a very, very long time, unless it's destroyed by carelessness or intention...which is true for any data storage medium. Have you ever seen an antique book, one that was printed before this country was born? Have you ever held one in your hands, and read it? I have. Not only is the "data" still as readable as the day it was printed, there is an emotional connection to its originator, and everyone else who's opened it since...but that's off the topic.
And the humble pencil -- graphite is a mineral pigment, and those have a "shelf life" measured in geological time. Same with archival inks.
It's not just text, but images. Ordinary snapshots, decently stored, last for generations; we still have the earliest photographs, made over a century and a half ago. But if Matthew Brady had had a modern digital camera, his visual record of the Civil War would be long since lost.
Bottom line: we're putting our "eggs" -- the shared memories of our civilization -- into a brand-new, oh-wow-cool high-tech basket that has about as much longevity as a TV dinner. I only hope that somebody, somewhere, is making hard copyies and tucking them away.