if you are using a Blue ring version, with a single disk, and you don't mind giving a small amount of money ,
you could use the MybookClone Feature which does the following :
Format your external SATA usb drive as ext2 ( linux type )
- Backup your Mybook System partition at a scheduled time
in case of HArd disk crash, simply replace the Mybook HDD with the external one
- backup your internal data to the external backup usb by mirroring it ( incremental backup using rsync).
The only thing is that the external drive needs to be of the same size as the internal one.
it needs to be a sata drive
This backup system intend to be a "Mirror" rather than backup files