[Samba] group mapping question

[Miguel Medalha]

>  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?
>

Yes.

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

 From a table in "Chapter 41. Managing TDB Files" of the 
"Samba-HOWTO-Collection" you just quoted:
http://us1.samba.org/samba/docs/man/Samba-HOWTO-Collection/msdfs.html

«
group_mapping.tdb: Stores group mapping information. Preserve?=Yes. Not 
used when using LDAP backend.
»

So, if you use LDAP, backup the LDAP database or a export it to a LDIF 
file and keep the file.
If you are using tdbsam as a backend, look into /var/lib/samba (at least 
in a RedHat System) and backup the "group_mapping.tdb" file.
 
Most of all, do your homework. Please note that you can download the 
following books in PDF format and use the search function.

Samba 3 By Example
Samba 3 HOWTO

They are included with Samba.