When copying to a NAS which uses an EXT2 or EXT3 file system, robocopy often copies files that haven’t changed. To fix this you need to use the /FFT flag to assume FAT file times (2 second granularity). Although the target folder is ext2/ext3, these file systems also implement file times with 2 second granularity.

If you get (ERROR 5), you need to turn off the attribute copying. Robocopy uses the /COPY:DAT by default, which means to copy data, attributes and timestamp. You should turn off attribute copying by explicit setting /COPY:DT.

So, the command to backup from a NTFS partition to a ext2/ext3 partition should be: