samba - Mar 2005 - idmap concern on migrate from samba-2 to samba-3

Hi,

I'm upgrading an Samba-2.2.7a PDC to Samba-3.0.11 and I want to add
a samba BDC to the domain. I've seen in the Samba-3 How-to, in the
chapter Backup Domain Control, the example of the "Minimal setup for
being a BDC" it includes idmap.

It's really necessary the use of idmap and winbind in a domain with two
samba DC's?

Thanks in advance.