Generally I shoot on an AF100 and download the SD cards using Shotput to a hard drive(LaCie 750 GB Firewire 800). Then I mirror to another drive using SuperDuper. When I do this smart copy to the other drive I often encounter a bad video file which has become corrupted and just won't transfer to the new drive. This has become my only way to discerning when I've downloaded a bad copy. Often I just redownload a new version of the card because I don't delete my cards until I have them in two locations. This works but it is far from ideal. Am I missing something that is making my files go corrupt or is there a better way of verifying when my files get corrupted?