timemachine and raid type

[Enquiries]

I just got a a ds916 and would like to set up for mac timemachine. Is there a raid type where I can back up across different drives where if one drive fails I don't loose all data? Or do I have to use SHR with redundnacy and having to use twice as many drives? Duplicating everything? I would also. like to be able to add more drives as my data grows. Note my schime involves also backing up to as separate system with the shr and redundancy but not the history and role back element of timemachine. Also with the NAS and its error checking would I be warned if one of the drives was dying if I opted for a system with the data striped across all drives?

thanks for your help. what would. you suggest