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.