Migration

It is a good idea to test as many steps as possible in advance using sandbox machines. Firewalls prevent the NT4 domain controller and the Active Directory domain controller from getting in each other's way during the migration. But if they do so, some manual attention is required, because the admin needs to convert each individual computer.

One fairly typical scenario is that the operator of NT4 DC runs the domain controller together with the file server on the same machine. Samba 4 won't let you do the server to this dual role, so the best approach is to let the file server run on the existing server and set up the domain controller on a virtual machine or another computer.

You also need to keep in mind that groups and users may use the same name in AD environments. Last but not least, administrators need to change the LDAP server integrated into Samba 4 via /etc/samba/smb.conf from localhost to the IP address of the old LDAP server. Use samba-tool domain classicupgrade [10] to switch to a full-fledged Samba 4 AD domain controller. Backing up configuration files is recommended, but the upgrade works with all password back ends, that is, smbpasswd, tdbsam, and ldapsam.

Admins should also understand that the change from a NT4 domain controller to Samba 4 is a one-way street; you cannot easily roll back. A methodical and granular approach is thus useful. Beginners might find it easier to just start with Samba 4 in the first place.

Conclusions

All told, Samba Version 4 is a viable alternative to Windows AD domain controllers, and it provides most of the features you would get with a Windows system. The performance should be absolutely adequate in environments without special configurations.

If you do not rely on the functionality of an AD domain controller and have deployed a Samba Classic domain without trouble for years, the only benefit you might actually experience after the migration is better network drive performance with Samba 4.