If you want to backup to your own devices, you gotta understand that, other than the iDrive, which I just learned about, the backup can only be done to local directory.

So, since MangoES runs on Debian, you just have to mount whatever external device to a local directory, and with the Mango GUI, point the backup to that directory.

Using this method you can backup to basically anything, since Debian has the ability to mount just about anything.

For example, we backup to a NAS share, which we mounted to a local directory using fstab, so it mounts at boot automatically.