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    Software Defined Networks for SANs?

    Posted by David Fair

    Previously, I’ve blogged about the VN2VN (virtual node to virtual node) technology coming with the new T11-FC-BB6 specification. In a nutshell, VN2VN enables an “all Ethernet” FCoE network, eliminating the requirement for an expensive Fibre Channel Forwarding (FCF) enabled switch. VN2VN dramatically lowers the barrier of entry for deploying FCoE. Host software is available to support VN2VN, but so far only one major SAN vendor supports VN2VN today. The ecosystem is coming, but are there more immediate alternatives for deploying FCoE without an FCF-enabled switch or VN2VN-enabled target SANs? The answer is that full FC-BB5 FCF services could be provided today using Software Defined Networking (SDN) in conjunction with standard DCB-enabled switches by essentially implementing those services in host-based software running in a virtual machine on the network. This would be an alternative “all Ethernet” storage network supporting Fibre Channel protocols. Just such an approach was presented at SNIA’s Storage Developers Conference 2013 in a presentation entitled, “Software-Defined Network Technology and the Future of Storage,” Stuart Berman, Chief Executive Officer, Jeda Networks. (Note, of course neither approach is relevant to SAN networks using Fibre Channel HBAs, cables, and switches.)

    Interest in SDN is spreading like wildfire. Several pioneering companies have released solutions for at least parts of the SDN puzzle, but kerosene hit the wildfire with the $1B acquisition of Nicira by VMware. Now a flood of companies are pursuing an SDN approach to everything from wide area networks to firewalls to wireless networks. Applying SDN technology to storage, or more specifically to Storage Area Networks, is an interesting next step. See Jason Blosil’s blog below, “Ethernet is the right fit for the Software Defined Data Center.”

    To review, an SDN abstracts the network switch control plane from the physical hardware. This abstraction is implemented by a software controller, which can be a virtual appliance or virtual machine hosted in a virtualized environment, e.g., a VMware ESXi host. The benefits are many; the abstraction is often behaviorally consistent with the network being virtualized but simpler to manipulate and manage for a user. The SDN controller can automate the numerous configuration steps needed to set up a network, lowering the amount of touch points required by a network engineer. The SDN controller is also network speed agnostic, i.e., it can operate over a 10Gbps Ethernet fabric and seamlessly transition to operate over a 100Gbps Ethernet fabric. And finally, the SDN controller can be given an unlimited amount of CPU and memory resources in the host virtual server, scaling to a much greater magnitude compared to the control planes in switches that are powered by relatively low powered processors.

    So why would you apply SDN to a SAN? One reason is SSD technology; storage arrays based on SSDs move the bandwidth bottleneck for the first time in recent memory into the network. An SSD array can load several 10Gbps links, overwhelming many 10G Ethernet fabrics. Applying a Storage SDN to an Ethernet fabric and removing the tight coupling of speed of the switch with the storage control plane will accelerate adoption of higher speed Ethernet fabrics. This will in turn move the network bandwidth bottleneck back into the storage array, where it belongs.

    Another reason to apply SDN to Storage Networks is to help move certain application workloads into the Cloud. As compute resources increase in speed and consolidate, workloads require deterministic bandwidth, IOPS and/or resiliency metrics which have not been well served by Cloud infrastructures. Storage SDNs would apply enterprise level SAN best practices to the Cloud, enabling the migration of some applications which would increase the revenue opportunities of the Cloud providers. The ability to provide a highly resilient, high performance, SLA-capable Cloud service is a large market opportunity that is not cost available/realizable with today’s technologies.

    So how can SDN technology be applied to the SAN? The most viable candidate would be to leverage a Fibre Channel over Ethernet (FCoE) network. An FCoE network already converges a high performance SAN with the Ethernet LAN. FCoE is a lightweight and efficient protocol that implements flow control in the switch hardware, as long as the switch supports Data Center Bridging (DCB). There are plenty of standard “physical” DCB-enabled Ethernet switches to choose from, so a Storage SDN would give the network engineer freedom of choice. An FCoE based SDN would create a single unified, converged and abstracted SAN fabric. To create this Storage SDN you would need to extract and abstract the FCoE control plane from the switch removing any dependency of a physical FCF. This would include the critical global SAN services such as the Name Server table, the Zoning table and State Change Notification. Containing the global SAN services, the Storage SDN would also have to communicate with initiators and targets, something an SDN controller does not do. Since FCoE is a network-centric technology, i.e., configuration is performed from the network, a Storage SDN can automate large SAN’s from a single appliance. The Storage SDN should be able to create deterministic, end-to-end Ethernet fabric paths due to the global view of the network that an SDN controller typically has.

    A Storage SDN would also be network speed agnostic, since Ethernet switches already support 10Gbps, 40Gbps, and 100Gbps this would enable extremely fast SANs not currently attainable. Imagine the workloads, applications and consolidation of physical infrastructure possible with a 100Gbps Storage SDN SAN all controlled by a software FCoE virtual server connecting thousands of servers with terabytes of SSD storage? SDN technology is bursting with solutions around LAN traffic; now we need to tie in the SAN and keep it as non-proprietary to the hardware as possible.

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