Upgrading to samba 4.2

[Daniele Dario]

Hi list,
I'm looking for the safest way to upgrade my two samba 4.1.14 DCs to
4.2.1. From the tarball I saw that the only advice is to backup the
sensible folders (private, etc, var, sysvol) before to run make install
but in a scenario with more than one DC I think that it should be better
to trust on the second DC than use a backup am I right?
Other question: one of the two DCs acts also as a fileserver. Is there
something I have to take in account before/while upgrading?

Thanks in advance,
Daniele.