The SMB protocol is mainly known as the basis for file sharing in Windows and is familiar to Samba and Linux users, too. Windows 8.1 and Windows Server 2012 R2 use the new Server Message Block 3 (SMB 3) protocol, which has several advantages over the legacy version. Although it was already introduced with Windows Server 2012, it was once again improved in Windows Server 2012 R2. Rapid access to network storage especially benefits enterprise applications, such as SQL Server and virtual disks in Hyper-V.

The disks of virtual servers can reside on the network with Windows Server 2012 R2, for example, on file shares or iSCSI targets. Saving large files  – like the disks of file-based virtual servers on the network – offers some advantages over block-based storage, including easier management. This is especially true if the files are stored in file shares, because you don't need to use external management tools or to change management workflows.

Windows Server 2012 R2 lets you use VHDX files as an iSCSI target. This means that Hyper-V hosts can store their data on iSCSI disks, which are in turn connected via SMB 3. VHDX files are also much more robust and allow sizes up to 64TB.

SMB 3 can forward SMB sessions belonging to services and users on virtual servers in clusters. If a virtual server is migrated between cluster nodes, the sessions remain active; users are not cut off from services during this operation. Thus, in addition to higher performance and better availability, SMB 3 also supports high availability.

New in SMB 2.0 and 2.1

SMB was initially developed by IBM and integrated by Microsoft into Windows in the mid-1990s via LAN Manager. Microsoft modified SMB 1.0 and submitted it to the Internet Engineering Task Force (IETF), and SMB was renamed to CIFS (Common Internet File System).

Microsoft immediately started improving SMB after taking it over from IBM. Microsoft added some improvements in version 2.0 of Windows Vista and version 2.1 of Windows 7 and Windows Server 2008. As of version 2.0, Microsoft no longer uses the term CIFS, because the original extensions were developed for SMB 1.0, and they no longer play a role in SMB 2.0.

SMB 2.1 mainly offers performance improvements, especially for very fast networks in the 10Gb range. The version supports larger transmission units (Maximum Transmission Units, MTUs). Additionally, the energy efficiency of the clients was improved. Clients from SMB 2.1 can switch to power saving mode despite active SMB connections.

Improvements in SMB 3.0 include, for example, TCP Windows Scaling and accelerations on the WLAN. Microsoft also optimized the connection between the client and server, and improved the cache on the client. With the new pipeline function, servers can write multiple requests to a queue and execute them in parallel. This new technology is similar to buffer credits in Fibre Channel technology.

Microsoft has extended the data width to 64 bits in the current version, allowing block sizes greater than 64KB, which accelerates the transfer of large files, such as virtual disks or databases. Additionally, the optimized connections between the client and server prevent disconnections on unreliable networks such as WLAN or WAN environments.

What's New in SMB 3.0?

In Windows Server 2012, Microsoft introduced SMB version 2.2 with further improvements. Later, these innovations were deemed so far-reaching that the version was subsequently increased to 3.0. One new feature in SMB 3.0, for example, is server-based workloads, which are supported for Hyper-V and databases with SQL Server 2012/2014.

Hyper-V for SMB can now handle Universal Naming Convention (UNC) paths as the location of the control files on virtual servers. Also, virtual disks can now use UNC paths; that is, they can save files directly on the network. Simply put, this means that the location of the virtual disks on Windows Server 2012 or newer can be a UNC path, so you don't need to use drive letters or map network drives. For example, you can now address the data via a service name; there is no longer a requirement for a physical server name, as for a normal drive letter.

SMB 3.0 in the Enterprise

SMB 3.0 is much more robust, more powerful, and more scalable and offers more security than its predecessors, which is especially important for large environments. For example, SMB Transparent Failover allows clients to connect to a file server in a cluster environment. If the virtual file server is moved to another cluster node, the connections to the clients remain active. In the current version of SMB, open SMB connections are also redirected to the new node and remain active. The process is completely transparent to clients and Hyper-V hosts.

If virtual disks are stored on file shares in a cluster, services are no longer interrupted when the server is migrated. Another new feature in SMB 3.0 is SMB multichannel, in which the bandwidth is aggregated from multiple network adapters between SMB 3 clients and SMB 3 servers. This approach offers two main advantages: The bandwidth is distributed across multiple links for increased throughput, and the approach provides better fault tolerance if a connection fails. The technology works in a similar way to multipath I/O (MPIO) for iSCSI and Fibre Channel networks.

SMB Scale-Out file servers use Cluster Shared Volumes (CSV) for parallel access to files across all nodes in a cluster, which improves the performance and scalability of server-based services, because all nodes are involved. The technology works in parallel with features such as transparent failover and multichannel.

Additional SMB performance indicators let admins measure usage and utilization of file shares, including throughput, latency, and IOPS management reporting. The new counters in the Windows Server 2012 and Windows Server 2012 R2 performance monitoring feature support metrics for the client and server so that analysis of both ends of the SMB 3.0 connection is possible. These new technologies are useful for troubleshooting performance issues and for ensuring stable data access on the network.

The new SMB encryption lets you encrypt the data in SMB connections. This technology is only active if you use SMB 3.0 clients and servers. If you use legacy clients with SMB 2.0 and SMB 1.0 in parallel, encryption is disabled.