If you are using a USB (thumb) drive to backup files from your Windows NTFS file system, and you are using some intelligent backup program, like robocopy, which only backup files with different time stamp (backup only newer or older files), you will end up with backing up ALL files each time right after daylight saving time status changes. Why it loses intelligence some time?

It is because by default, USB drives are FAT file system which stores the last file modified time by using Local Time, while the NTFS file stores the last file modified time by using UTC time. So when the daylight saving time status changes, NTFS file timestamp will change, but FAT file timestamp will not, that causes one hour of time difference.

And that one hour difference will cost you re-copy all the files you haven’t change. It happens twice a year.