I found rsync redoing files that have no modification. One file is >1gb so it takes a bit to do. My command is below. I'm running the command via ssh. The filesystem in question is a NTFS usb HDD to a ext3 filesystem. Both connected to the same virtual machine running ubuntu
rsync --stats --progress -r src dst
rsync -aunless you know there's something you don't want to preserve. Without any options, you're askingrsyncto not preserve times, so it can't use the modification time as an optimization not to copy the file the second time.