Starting from the first release of the Samba Server Version 4 (4.0.0), the software now supports the SMB file that serves the protocol Version 2.1 of Microsoft; it also provides preliminary support for the SMB protocol Version 3.0 [18]. The SMBv2.1 has been a great achievement for the Samba project since the introduction of the SMBv2.0 on Samba Version 3.6. Major improvements that Version 2.1 brings, as compared to Version 2.0 (from the Microsoft announcement), are mainly performance enhancements [19], listed as follows:
Client oplock leasing model
Large MTU support
Improved energy efficiency for client computers
Support for previous versions of SMB
Tip
You can read more about the changes between the protocol Versions 2.0 and 2.1 and more about each individual feature at the official Microsoft reference [19]: http://technet.microsoft.com/en-us/library/ff625695%28v=ws.10%29.aspx
The official Samba 4 release announcement has some important information...