[Samba] Samba4 Can we use two file-servers?

[steve]

Hi
We've just added a second DC to our domain, both DCs are Samba4

DC1 is also the s3fs file server. If that goes down then so does the 
file-server. IOW, we can still authenticate via DC2 but we cannot do any 
work!

What are my options here? Is it possible to sync the files to DC2 and 
use that in case of failure? Or maybe add a third box running smbd?

Cheers,
Steve