I have a 750GB Passport Essential that is scheduled to backup once a week. It takes more than 6 hours to backup approximately 160GB. I have done all of the firmware updates and have the most recent (1.6.4) Smartware. It seems to completely backup my data rather than just backing up new or changed items. I have it programmed to only keep 2 copies, but it keeps each backup. I run Windows 7 (64-bit) and the drive is less than 6 months old. I it plug it into my USB/eSATA port. I have run the Data Lifeguard and it passed. I hope someone can help me figure out what is going on–I had a smaller capacity Passport and everything worked fine on it until it wore out.
Smartware does not have the option to schedule backups AFAIK
what software are you using?
If using Win Backup, it might do an entire drive backup each and every time