I'd like to have two backups of my hard drive. When I use Windows Backup and Restore on Windows 7 it backs up only the files that have not been backed up yet. That's great. Its fast.

I also have a Clickfree C6 backup drive that will do the same. I'm concerned that, 15 years ago, backup programs used a file attribute that changed to indicate a file had been backed up already. If this method is still being used, when I backup to the second drive, that attribute will indicate the file has already been backed up and won't put it on my second drive. Is this correct.

I don't want to have to do a complete backup on the second drive if not necessary.