samba - Nov 2009 - posix user mapped to window users without idmap ?

Dear all

    I am using samba+ldap as PDC , now i want a create a BDC that takes over
domain logon process  process when PDC become down by taking users/groups
information from slave ldap server . My shares are present on disk which is
accessible both by PDC and BDC and permission given to POSIX uesrs and group
which i think internally mapped to samba users/groups.
Now since ldap storing posix users/groups as well as samba users/group so is
any need to configure IDMAP in smb.conf ?

Does slave ldap server not map posix users/groups to samba users/groups
correctly without configuring IDMAP ?

Thanks

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