[Samba] group mapping question

[MargoAndTodd]

Hi All,

Just a general question about groups.  I am upgrading a
Samba workgroup, server to a PDC.  I have been reading:

http://us1.samba.org/samba/docs/man/Samba-HOWTO-Collection/groupmapping.html#id2589321

In this link, they tell of how to map a windows group to
a Samba group

  net groupmap add ntgroup="Domain Admins" unixgroup=domadm rid=512 type=d

Question 1: if my previous /etc/group names already match the
ntgroup names, do I still need to run the above command?

Question 2: once I have mapped these groups, where are they
stored, so I can back them up?

Many thanks,
-T