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If you look at the history of the Server Message Block (SMB) protocol, you get an idea that it has widely been used to provide file services to the SMB clients. An SMB client makes requests for accessing, reading and writing to file shares residing on an SMB server. It depends on the SMB server component as to what it has to offer when an SMB client requests for file services. SMB server components running on Windows Server 2012 or later have a lot to offer for SMB clients. Microsoft has taken a step further in the development of the SMB protocol in Windows Server 2012 and introduced enterprise grade features that not only have helped reduce the cost for small and midsize businesses, but has also become a strong selling point for Hyper-V server virtualization.
Initially, SMB was known for just file sharing, but starting with Windows Server 2012, there have been significant changes in the SMB protocol 3.0, including SMB Direct, SMB Multichannel (multiple connections per SMB session), SMB Transparent Failover, SMB Scale-Out, SMB Directory Leasing and many more. In Windows Server 2012 R2, a new version of SMB 3.02 was introduced that included significant changes including improved performance of SMB Direct, improved SMB bandwidth management, and enabling Hyper-V live migration of VMs and VM storage without failover clustering to name a few.
Achieving high availability of Hyper-V VMs without block-based storage: One benefit that boosts the return on investments is the use of SMB file shares as a shared storage for Hyper-V hosts. This is sometimes referred to as "Hyper-V over SMB." In earlier versions of Hyper-V you had to store Hyper-V VMs on a block-based storage to achieve high availability of the VMs. In Windows Server 2012 and later OSes, you can configure SMB file shares to host Hyper-V VM files such as VM configuration, virtual hard disks and snapshot files and expect the same reliability, availability and high performance that you achieve using block-based storage. When implemented as a shared storage on Windows Server 2012 or later, SMB helps deploy a Hyper-V server virtualization infrastructure without spending precious IT dollars on expensive SAN devices. There are several other Hyper-V scenarios where SMB can be a useful. You can create a file server cluster running on Windows Server 2012 or later, create SMB shares, configure the available properties for the SMB shares, and then have the SMB shares available for Hyper-V hosts for hosting the VM files.
If you deploy VM files over an SMB share created on Windows Server 2012 or later file servers, the SMB Transparent Failover feature can help you provide continuous availability of VMs in case of any maintenance activity for one of the clustered nodes in a file server cluster. This is achievable by implementing SMB Scale-Out file server cluster. A scale-out file server hosts SMB shares that are simultaneously online on all the nodes in a file server cluster.
Reducing operational expenditure: You can manage file shares instead of requiring someone with expertise to manage storage fabric and LUNs which, in turn, helps you reduce the operating expenditures associated with managing a SAN environment. A virtual administrator who knows how to manage a file share can easily manage SMB shares rather than requiring another administrator to manage the complex SAN environment.
SMB as a shared storage for VHDX file sharing: The VHDX file sharing feature of Hyper-V helps you implement guest clustering without exposing SAN storage to Hyper-V guests. The VHDX file that will be shared among the multiple VMs must be kept on a shared storage. Since an SMB share created on Windows Server 2012 or later can act as a shared storage, you can implement guest clustering without requiring storage from a SAN. Note that to use the VHDX file sharing feature, you would need to host VMs on a Windows Server 2012 R2 Hyper-V host.
Some Hyper-V features use SMB: It is worth mentioning that SMB has a role to play for some of the notable Hyper-V features such as Storage Live Migration and Shared Nothing Live Migration introduced in Windows Server 2012. Neither of those features require Windows failover clustering to be implemented to utilize the SMB 3.0 capabilities to move VM and its storage while the VM is running. In case you have noticed a Hyper-V VM or a Storage Live Migration transfer without a Hyper-V failover cluster, it is the SMB 3.0 running on Windows Server 2012 R2 that does the job in the background.
Faster Live Migration of VMs: Most of Hyper-V virtual administrators who are familiar with Hyper-V Live Migration and SMB Direct or "SMB over RDMA" will select SMB as the live migration protocol for transferring VMs to other Hyper-V hosts. It is because live migration over SMB takes advantage of RDMA network acceleration, which in turn gives you faster live migration.
A protocol for future virtualization: It is imperative to understand that Microsoft has been working continuously on the development of the SMB protocol in upcoming Windows Server 2016. There are a few new features in In Windows Server 2016 that help you run a secure SMB environment such as pre-authentication integrity and various encryption options for encrypted SMB connection. The SMB version that will be available in the upcoming Windows Server 2016 is SMB 3.1.1.
The minimum infrastructure required to deploy Hyper-V over SMB is that you obtain a copy of Windows Server 2012 or later, install File and Storage Services role, configure SMB share, and then have the SMB shares available to a standalone Hyper-V host or a Hyper-V cluster.
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