Originally posted by Tom S. but has one issue that drove me nuts. Each time you insert a card, it copies all the files on the card, even if you already copied them once. So if you used a 24GB card and backed it up when it was half full, then again when it was full, you would end up with the first half copied twice a total of 36GB of files on the drive. Of course with 500GB, it didn't really matter, just annoying.
Just look for portable data storage models that have
'incremental back up' in the product description. It will backup only the new data on card and skip previously saved data.