This page has been deprecated in favor of the Ubuntu Server Guide at https://ubuntu.com/server/docs
Specifically about samba, we have:
- Under https://ubuntu.com/server/docs/how-to: - How-to guides -> Networking -> Samba: file server, print server, share access controls, and more. 
- How-to guides -> Active Directory integration with winbind: preparing to join a domain, rid and autorid identity mapping backends, simple domains and forests. 
 
- Under https://ubuntu.com/server/docs/explanation: - Explanation -> Active Directory integration: choosing an identity mapping backend, what are SIDs, which idmap backends to pick under which circumstances, details about the rid and autorid backends.