SMB 3.0 : All about it – Part I

Thought of writing a blog about SMB 3.0 and somehow it hit me to first talk about SMB from the very scratch and then move to SMB 3.0. 


What is SMB ?

Wikipedia definitions says - Server Message Block (SMB), also known as Common Internet File System (CIFS) operates as an application-layer network protocol mainly used for providing shared access to files, printer, serial ports, and miscellaneous communications between nodes on a network. It also provides an authenticated inter-process communication mechanism.

In other words, the Server Message Block (SMB) protocol is a network file sharing protocol that allows applications on a computer to read and write to files and to request services from server programs in a computer network. The SMB protocol can be used on top of its TCP/IP protocol or other network protocols. Using the SMB protocol, an application (or the user of an application) can access files or other resources at a remote server. This allows applications to read, create, and update files on the remote server. It can also communicate with any server program that is set up to receive an SMB client request.  

When it comes to implementation, SMB works through a Client-Server approach, where a client makes specific requests and the server responds accordingly. One section of the SMB protocol specifically deals with access to filesystems, such that clients may make requests to a file server; but some other sections of the SMB protocol specialize in inter-process communication (IPC). The Inter-Process Communication (IPC) share, or ipc$, is a network share on computers running Microsoft Windows. This virtual share is used to facilitate communication between processes and computers over SMB, often to exchange data between computers that have been authenticated.

The next phase arrives when Microsoft introduced a new version of the SMB protocol (SMB 2.0 or SMB2) with Windows Vista in 2006.

With introduction of new capabilities like pipelining, symbolic linking, caching etc, much better performance was achieved. Another major improvement was in terms of block size. The SMB1 protocol uses 16-bit data sizes, which amongst other things, limits the maximum block size to 64K. SMB2 uses 32 or 64-bit wide storage fields, and 128 bits in the case of file-handles, thereby removing previous constraints on block sizes, which improves performance with large file transfers over fast networks.


Windows Server 2012 includes a new feature called SMB Multichannel, part of the SMB 3.0 protocol, which increases the network performance and availability for File Servers. 

Will delve into details of each enhancement  capability in next part.


There are several different versions of SMB used by Windows operating systems:

  • CIFS – The ancient version of SMB that was part of Microsoft Windows NT 4.0 in 1996. SMB1 supersedes this version.
  • SMB 1.0 (or SMB1) – The version used in Windows 2000, Windows XP, Windows Server 2003 and Windows Server 2003 R2
  • SMB 2.0 (or SMB2) – The version used in Windows Vista (SP1 or later) and Windows Server 2008
  • SMB 2.1 (or SMB2.1) – The version used in Windows 7 and Windows Server 2008 R2
  • SMB 3.0 (or SMB3) – The version used in Windows 8 and Windows Server 2012

Windows NT is no longer supported, so CIFS is definitely out. Windows Server 2003 R2 with a current service pack is under Extended Support until 2015, so SMB1 is still around for a little while. SMB 2.x in Windows Server 2008 and Windows Server 2008 R2 will be around at least until 2018, when Extended Support for those products is scheduled to expire. You can find the most current information on the support lifecycle page for Windows Server. The information is subject to the Microsoft Policy Disclaimer and Change Notice.  You can use the support pages to also find support policy information for Windows XP, Windows Vista and Windows 7.


Negotiated Versions

Here’s a table to help you understand what version you will end up using, depending on what Windows version is running as the SMB client and what version of Windows is running as the SMB server:

Client / Server OS Windows 8
Windows Server 2012
Windows 7
Windows Server 2008 R2
Windows Vista
Windows Server 2008
Previous versions
of Windows
Windows 8
Windows Server 2012
SMB 3.0 SMB 2.1 SMB 2.0 SMB 1.0
Windows 7
Windows Server 2008 R2
SMB 2.1 SMB 2.1 SMB 2.0 SMB 1.0
Windows Vista
Windows Server 2008
SMB 2.0 SMB 2.0 SMB 2.0 SMB 1.0
Previous versions
of Windows
SMB 1.0 SMB 1.0 SMB 1.0 SMB 1.0



Using PowerShell to check the SMB version

In Windows 8 or Windows Server 2012, there is a new PowerShell cmdlet that can easily tell you what version of SMB the client has negotiated with the File Server. You simply access a remote file server (or create a new mapping to it) and use Get-SmbConnection. Here’s an example:

PS C:\> Get-SmbConnection
ServerName   ShareName  UserName            Credential          Dialect   NumOpens
----------   ---------  --------            ----------          -------   --------
FileServer1  IPC$       DomainName\UserN... DomainName.Testi... 3.00      0
FileServer1  FileShare  DomainName\UserN... DomainName.Testi... 3.00      14
DomainCtrl1  netlogon   DomainName\Compu... DomainName.Testi... 2.10      1

In the example above, a server called “FileServer1” was able to negotiate up to version 3.0. That means that both the client and the server support the latest version of the SMB protocol. You can also see that another server called “DomainCtrl1” was only able to negotiate up to version 2.1. You can probably guess that it’s a domain controller running Windows Server 2008 R2.

If you just want to find the version of SMB running on your own computer, you can use a loopback share combined with the Get-SmbConnection cmdlet. Here’s an example:

PS C:\> dir \\localhost\c$
Mode                LastWriteTime     Length Name
----                -------------     ------ ----
d----         5/19/2012   1:54 AM            PerfLogs
d-r--          6/1/2012  11:58 PM            Program Files
d-r--          6/1/2012  11:58 PM            Program Files (x86)
d-r--         5/24/2012   3:56 PM            Users
d----          6/5/2012   3:00 PM            Windows

PS C:\> Get-SmbConnection -ServerName localhost

ServerName  ShareName  UserName            Credential          Dialect  NumOpens
----------  ---------  --------            ----------          -------  --------
localhost   c$         DomainName\UserN... DomainName.Testi... 3.00     0

Please note that you have about 10 seconds after you issue the “dir” command to run the “Get-SmbConnection” cmdlet. The SMB client will tear down the connections if there is no activity between the client and the server. It might help to know that you can use the alias “gsmbc” instead of the full cmdlet name.



Practical Applications  

      Some new practical ways to use the new SMB 3.0 protocol could be -

      1) File storage for virtualization (Hyper-V™ over SMB). Hyper-V can store virtual machine files, such as configuration, Virtual hard disk (VHD) files, and snapshots, in file shares over 

          the SMB 3.0 protocol. This can be used for both stand-alone file servers and clustered file servers that use Hyper-V together with shared file storage for the cluster.

      2) Microsoft SQL Server over SMB. SQL Server can store user database files on SMB file shares. Currently, this is supported with SQL Server 2008 R2 for stand-alone SQL servers.  

         Upcoming versions of SQL Server will add support for clustered SQL servers and system databases.

     3)Traditional storage for end-user data. The SMB 3.0 protocol provides enhancements to the Information Worker (or client) workloads. These enhancements include reducing the  

        application latencies experienced by branch office users when accessing data over wide area networks (WAN) and protecting data from eavesdropping attacks.

Features and Capabilities

Here’s a very short summary of what changed with each version of SMB:

  • From SMB 1.0 to SMB 2.0 - The first major redesign of SMB
    • Increased file sharing scalability
    • Improved performance
      • Request compounding
      • Asynchronous operations
      • Larger reads/writes
    • More secure and robust
      • Small command set
      • Signing now uses HMAC SHA-256 instead of MD5
      • SMB2 durability


  • From SMB 2.0 to SMB 2.1

                    File leasing improvements

                    Large MTU support



  • From SMB 2.1 to SMB 3.0


    • Availability
      • SMB Transparent Failover
      • SMB Witness
      • SMB Multichannel
    • Performance
      • SMB Scale-Out
      • SMB Direct (SMB 3.0 over RDMA)
      • SMB Multichannel
      • Directory Leasing
      • BrachCache V2
    • Backup
      • VSS for Remote File Shares
    • Security
      • SMB Encryption using AES-CCM (Optional)
      • Signing now uses AES-CMAC
    • Management
      • SMB PowerShell
      • Improved Performance Counters
      • Improved Eventing

Hope this has given you a start for SMB & what's coming with SMB 3.0. More in following posts.

Comments (2)

  1. Anonymous says:

    Wasn't logged in when I posted that.  How can I get in touch with you?

  2. Pracheta says:

    Can be connected on twitter, handle is @prachetab

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