With Raid 0, the data is written to both hard disks in parallel, thus increasing the read and write speed. With the 2X4TB system, you also have the full 8 TB available. If it is configured as Raid 1, the data is mirrored. The disadvantage - apart from the loss of speed - is that "only" 4TB are available, but since the data are mirrored, the reliability is increased. This means that if one hard disk gives up the ghost, the data is still available on the second one. This is why Raid 1 is called a redundant system.
Unfortunately, we could not find any precise information on this from the manufacturer. The question has therefore been forwarded to our community so that someone who knows more about it can answer it.