Hi,
I'm backuping several disks to a local backup drive via rsnapshot, and then from time to time backuping the local backup drive to an external USB drive via the USB Backup plugin.
Surprised by the abnormal time it took the first time to rsync to the external usb drive, I realized that rsync was "duplicating" / "unlinking" the hard links created by rsnapshot. The solution (currently running on my NAS) is to add "-H" into the optional settings (-H = preserver hard link).
As this looks like a usual scenario, a checkmark in the USB backup settings page could be welcomed...