SNIA’s 18th Storage Developer Conference is officially a success, with 124 general and breakout sessions; Cloud Interoperability, Kinetic Storage, and SMB3 plugfests; ten Birds-of-a-Feather Sessions, and amazing networking among 450+ attendees. Sessions on NVMe over Fabrics won the title of most attended, but Persistent Memory, Object Storage, and Performance were right behind. Many thanks to SDC 2016 Sponsors, who engaged attendees in exciting technology … Continue reading
We had a tremendous response to our recent Webcast “Use Cases for iSCSI and FCoE – Where Each Makes Sense.” We had a lot of questions that we didn’t have time to address, so here are answers to them all. If you think of additional questions, please feel free to comment on this blog.
Q. You stated that FCoE requires End to End DCB connectivity. That is not entirely true if you have native Fibre Channel storage.
Once native FC is added, it is a hybrid FCoE/native FC network, not a simple FCoE network. To be clearer I could’ve stated that for FCoE all Ethernet links traversed must be DCB enabled.
Q. Any impact on the protocol choice if you bring SDN solutions with overlay networks using VXLAN or NVGRE within virtual switching in hypervisors into the picture?
An excellent question, but complicated enough that it probably deserves a discussion on its own. Overlay networks encapsulate Ethernet frames into routable packets. On a view of strict adherence to ISO ordering, that means L2 constructs like Data Center Bridging become “invisible” until decap. You lose the “lossless,” low-latency that FCoE expects and iSCSI may be taking advantage of, depending on your implementation. That doesn’t really favor one protocol over the other, but FCoE may lose advantages it has over iSCSI when confined to a single L2 subnet. But, unfortunately, the real answer to your question requires that you investigate in detail how the system software you are using handles encapsulated storage packets for both block storage protocols. Microsoft’s Hyper-V is different from VMware’s vSphere, and each flavor of SDN could be different as well. Proceed with caution.
Q. Have you heard of any enterprise customers who are interested in NIC Partitioning to separate iSCSI, FCoE, and typical network traffic? If so, can you provide information about those customers’ use cases?
We have not come across many customers that are interested in large-scale deployments yet.
Q. What are the use cases for using standalone FCoE switches in SAN keeping aside Cisco UCS and Blade Servers?
There are two ways to look at this:
1) To use FCoE as an end-to-end (Initiating server to target storage array) solution instead of, or to replace, Fibre Channel. Although, not very prevalent to date, the reason this option is chosen is to create a single converged LAN/SAN network that essentially retains the native FC constructs. The potential benefit would be in reduction in the amount of equipment required and the resources needed to deploy and administer two separate networks. This can be done in a phased approach, that uses multiprotocol switches, able to be used as Ethernet, FC or both on every port. This will provide future proofing, reduced qualification costs, and lower OPEX by no longer requiring the purchase of multiple switches of different protocols.
2) To continue the use of FC for connectivity from the Top of Rack switch to the storage arrays, but use FCoE connectivity for server access. This is much more prevalent, and even when deployed outside of the Cisco UCS blade servers, is used to increase flexibility in highly virtualized server environments or multi-tenancy, where workloads/VMs from the same physical servers need to connect to different storage types.
Q. How do iSCSI and FCoE switches handle redundancy? With FC, it is a best practice to implement dual fabrics with each storage system and server with paths down each.
Physical topology can be identical. A storage system has one set of targets (either IP addresses or FCoE targets) on one switch and other targets on the other switch. The initiators are configured to see any targets available on that leg.
To prevent Ethernet broadcast storms, technologies like per VLAN Spanning Tree and link aggregation are used. TRILL can also be used. For more details, I recommend reading this blog post by J Metz of Cisco. http://blogs.cisco.com/datacenter/understanding-fcoe-and-trill-the-easy-way/
Q. Doesn’t increasing CPU mean software processing for FCoE and iSCSI at both endpoints can reduce costs considerably (i.e. no full HBA functionality needed at the endpoints)?
Absolutely. If you have CPU cycles to spare at both endpoints, there is no reason to take on the extra cost of offload. However, remember the principle behind Moore’s law also works on things like network adapters and HBAs. It isn’t unreasonable to think that full offload capabilities will be included by default in a few years as technology progresses. And even if they aren’t, the actual application of Moore’s law will push the difference in CPU utilization to be trivial.
Q. How do large data centers configure and manage iSCSI? Is it by configuring the initiators and targets? My understanding is that most installations don’t use iSNS. Is this true?
It is true that most implementations of iSCSI don’t use iSNS. iSCSI initiators are simply configured with the target address by the administrator. In the FC world, SNS is simply there, but the iSCSI equivalent, iSNS, has always been optional. (SNS stands for Simple Name Service. It is a service that helps initiators find targets.)
Q. I have been doing a lot of testing to compare iSCSI to FC and noticed that as we move from traditional storage to SSD-based storage the IOPS increase faster for FCoE. For example, 18K+ for FCoE vs. 12K for iSCSI. Have you seen similar results?
I have seen some similar results. However, I’ve also seen some that don’t necessarily line up with that. I haven’t had the time to research this topic. Sounds like a good topic for a future post.
Q. Do you have any information about the number of customers who use FCoE Boot and iSCSI Boot?
Unfortunately I don’t. I do have anecdotal evidence to support customers using full-offload are more likely to boot from SAN. Since more full-offload FCoE adapters are in use that full-offload iSCSI adapters today, it makes sense that more are booting over FCoE than iSCSI, but again, I don’t have any evidence to support that.
Q. What about iSCSI over RoCE?
There are three network/fabric technologies that use RDMA: InfiniBand, iWARP, and RoCE. You can run iSCSI over any of these using the open-source iSER code supported by the Open Fabrics Alliance (https://www.openfabrics.org ). iSER has been written to OFA’s “verbs” for RDMA (rather than to the more familiar “sockets). However, note that of these three underlying transports, only iWARP is truly routable in general. So technically you could implement iSER on InfiniBand or RoCE but it may not do for you what you expect iSCSI to do for you, i.e., go anywhere the internet goes.
Q. How does FCIP compare with iSCSI for long distance requirements?
FC networks rely on guaranteed packet delivery to deliver low latency, predictable performance. IP networks are a best effort network allowing for dropped packets with transmission retries. Given the possibility of latency loss, FCIP has experienced limited adoption. Useful where required. But, typically not a core part of infrastructure. If cost is a concern and long distance is required as part of the solution, then iSCSI is the better choice as it designed to allow for lossy networks.
Q. Slide 22 – Was that hardware based iSCSI or software based iSCSI?
What was shown in the chart was software-based iSCSI, however you would see similar results with hardware-based iSCSI.
Q. What about FC vs FCoE performance? Any numbers?
Both Fibre Channel and FCoE can achieve line rate. Here’s an example of testing Yahoo! did on an 8Gb FC HBA and a 10 GbE CNA that showed exactly that result: http://www.intel.com/content/www/us/en/network-adapters/10-gigabit-network-adapters/10-gbe-ethernet-yahoo-case-study.html . So as Fibre Channel moves to 16 Gbps, it will outperform a 10GbE CNA, at least for peak performance. However, the tables turn with a 40 GbE CNA, several of which are in production now.
Q. Do you see SR-IOV used currently or in the future to separate FCoE or iSCSI from standard LAN traffic?
So far we have seen that with the exception of a few operating systems (e.g., AIX), SR-IOV support today is network only. Additionally, most customers want guaranteed bandwidth for storage and they wouldn’t be willing to run it on the same port as heavy NIC traffic.
Q. Are you aware of any FCoE targets for Windows?
I’m not aware of any right now.
Q. What is the max IOPS (at 4K) you can push thru 10G FCoE and iSCSI? Max latency (at 512 bytes)?
Latency is not determined by the pipe.
Q. Does FCoE really require a CNA? What about software only FCoE drivers?
Open FCoE does exist, but most FCoE implementations today use CNAs. I do expect the adoption of FCoE software solutions to increase fairly substantially. A lot of it comes down to the choice of booting via FCoE or another method.
Q. Do you think that the difference in FCoE/iSCSI usage for different App tiers can be related to the performance of the protocols?
Objectively, no. Either protocol implemented can be configured to hit or exceed a performance number. In my opinion, market perception of the protocols has more to do with the tier assignment than anything technical.
Q. Doesn’t 32 GbFC make it competitive with 40GbE FCoE?
From a purely technical perspective it helps, but FCoE is often deployed to reduce costs by simplifying cabling and switching by converging IP and storage onto the same fabric. 32Gb FC is slower than 40Gb and does nothing to reduce costs. Unless 32Gb FC is significantly less expensive than 40 Gb Ethernet on a per port basis, market forces are going to push towards Ethernet. There are still plenty of cases where organizations may deploy 32Gb FC instead of FCoE, but again, those criteria will mostly be non-technical.
Thanks to all my SNIA-ESF colleagues and Dell’Oro Group for helping me with these answers. If you missed the original Webcast, you can watch it on-demand here. You can also download a copy of the slides.
Why the FCoE – iSCSI Debate Continues
This is my first blog post for SNIA-ESF. As a Principal Storage Architect, I have been doing extensive research on the factors that are driving FCoE vs. iSCSI choices over the last several years. The more I dive into the topic, the more intriguing the debate becomes. In fact, this blog is a preview of an upcoming white paper I’m writing and a Webcast SNIA is hosting on February 18th. If you agree this debate is interesting, I encourage you to attend. Details on the Webcast are at the end of this post.
A Look Back at FCoE and iSCSI History
There are two entrenched standards for block storage protocols over Ethernet networks. FCoE was ratified in 2009, while iSCSI was ratified in 2004. Of course, various vendors and early adopters supported these protocols before ratification, so the history of these protocols is a couple of years longer than it looks, respectively. While iSCSI simply encapsulates the SCSI protocol in IP, FCoE operates lower in the network stack and to do so required many enhancements to Ethernet. While iSCSI runs on any IP network (mostly Ethernet these days), FCoE requires Data Center Bridging and Converged Network Adapters all running at 10 Gbps or faster.
All of the Data Center Bridging enhancements that make FCoE possible, like lossless Ethernet, benefit all of the protocols using Ethernet as the transport protocol. DCB doesn’t just make FCoE possible, but it improves iSCSI at the same time (see the SNIA-ESF blog, How DCB Makes iSCSI Better). So given that modern servers, networks, and storage may all be connected by hardware capable of running FCoE, that same network is also able to run iSCSI, as well as other network traffic. Nothing precludes them from running simultaneously on the same network either. The leading storage vendors that offer both FCoE and iSCSI target systems allow administrators to present the same LUN over either protocol with little effort, so a transition from one protocol to the other is not difficult.
Strengths and Weaknesses
So which network protocol is the right choice?
Each protocol has strengths and weaknesses when judged relative to each other. FCoE has higher throughput at lower host CPU utilization than iSCSI and FCoE doesn’t have to process the TCP/IP stack as iSCSI does. iSCSI is relatively simple to setup and troubleshoot when compared to FCoE because zoning is not a factor and IP connectivity (although not optimized for storage traffic) is likely in place already. Also, while FCoE has a comprehensive set of existing tools available to ease troubleshooting, there aren’t as many qualified people to use them in most enterprises. Ease of use, plus the ability to use low cost NICs and switches, gives iSCSI a cost advantage. (However, if you check out our SNIA-ESF webcast, “How VN2VN Will Help Accelerate Adoption of FCoE,” you’ll hear about new technologies that reduce the costs of deploying FCoE.) FC, and by extension FCoE, are perceived to be enterprise-grade, suitable for all workloads; and while iSCSI is being widely adopted at the enterprise level, it is still perceived by some not to be ready for Tier-1 applications. The graph below is excerpted from the report “Intel 10GbE Adapter Performance Evaluation” prepared by Demartek for Intel in September 2010. This data is consistent with the rest of the report findings and is only intended to be representative of the results from comparative iSCSI and FCoE testing. The report is interesting reading and I recommend looking at it for more information. This graph shows IOPS and CPU utilization for JetStress tests running against NetApp storage over multi-path iSCSI and FCoE. Note that latencies were all similar and running the tests against EMC storage showed similar results.
Many other factors must be considered, but according to industry pundits- as well as my own personal experience – in the majority of cases either protocol is adequate for the task at hand, and that is to effectively transfer block data across an Ethernet network.
The reality is, most servers, applications, and storage arrays simply won’t take advantage of FCoE’s superior performance or any storage protocol running over 10GbE. iSCSI and NAS protocols are very fast and are typically sufficient to meet most application requirements. But this is not meant to be a SAN vs NAS post – besides years of history, thousands of happy end users, and billions of continued investment show that both work well enough to meet most business needs. The commonly deployed storage systems and hosts are simply not configured with enough hardware to saturate multiple 10 gigabit network links. While this is rare today, it is going to become more common to see systems capable of saturating 10GbE pipes in the near future, especially as flash memory, either in all-flash arrays or tiered storage systems, find more application. (Hear more on the impact of flash in our SNIA-ESF webcast, “Flash – Plan for the Disruption”). At least as it relates to spinning media disk systems – network bandwidth increases faster than storage system throughput can keep up. So consider the storage system to be the bottleneck or limiting factor when evaluating storage network performance. After all, in most data center environments, the ratio of servers and applications to storage systems is high. So, it’s reasonable to expect the storage system to be the bottleneck. The absolute throughput of FCoE and iSCSI, when pushing a storage system to its limits, is not sufficient alone to be used as the sole basis for the decision between the two protocols except, for a few edge cases. Bottom line: Whether the storage system is the bottleneck or the network is the bottleneck the performance relationship between FCoE and iSCSI does not change.
These edge cases tend to be extremely IO intensive database workloads and big data applications, such as Hadoop. Citing the graph above, FCoE is about 15-20% faster on identical hardware than iSCSI. Granted this is a single graph of a single test, but the data is consistent across tests performed by IBM using Emulex network interfaces. If absolute throughput and efficiency (both network and CPU) are the only criteria when deciding between block protocols, FCoE looks like the choice. Since these cases are rare – because complexity, supportability, and even politics are almost always considered – the decision is not so obvious. Again, beyond the scope of this article, NAS protocols should be considered when determining the proper protocol for an application also.
Is There a Clear Winner?
While FCoE can claim technical superiority, iSCSI has the edge in cost and supportability. The number and range of systems supporting iSCSI connectivity is greater, particularly at the entry level. What’s more, the availability of people that can troubleshoot end-to-end connectivity for iSCSI is also much greater. (The “ping” command diagnoses most iSCSI connectivity problems.) Also, do a resume search on Monster or LinkedIn and the number of people that can configure VLANs dwarfs the number that can properly zone a Fibre Channel network. Greater familiarity reduces the support and operating cost of iSCSI.
IDC predicts that FCoE revenue will ramp very quickly through 2016. (If available to you, see the IDC Worldwide Enterprise Storage Systems 2012-2016 Forecast Update.) As customers decide to transition existing Fibre Channel networks to an Ethernet infrastructure, deploying FCoE would be a comfortable choice due to existing IT expertise and functional expectations of the Fibre Channel protocol.
Both iSCSI and FCoE are capable storage protocols and choosing one over the other will likely be dependent upon budget, IT skill set, and application requirements
Don’t forget to join us on Feb. 18th
Again, I encourage you to attend our February 18th Webcast, “Use Cases for iSCSI and FCoE –Where Each Makes Sense.” Analysts from Dell’Oro Group will share their latest market research on this topic and I’ll dive into use cases for both iSCSI and FCoE. It’s a live event, so please come with your toughest questions. I hope you’ll join us!
It’s been a bit of a bumpy ride for FCoE, which started out with more promise than it was able to deliver. In theory, the benefits of a single converged LAN/SAN network are fairly easy to see. The problem was, as is often the case with new technology, that most of the theoretical benefit was not available on the initial product release. The idea that storage traffic was no longer confined to expensive SANs, but instead could run on the more commoditized and easier-to-administer IP equipment was intriguing, however, new 10 Gbps Enhanced Ethernet switches were not exactly inexpensive with few products supporting FCoE initially, and those that did, did not play nicely with products from other vendors.
Keeping FCoE “On the Single-Hop”?
The adoption of FCoE to date has been almost exclusively “single-hop”, meaning that FCoE is being deployed to provide connectivity between the server and the Top of Rack switch. Consequently, traffic continues to be broken out one way for IP, and another way for FC. Breaking out the traffic makes sense—by consolidating network adapters and cables, it adds value on the server access side.
A significant portion of FCoE switch ports come from Cisco’s UCS platform, which runs FCoE inside the chassis. In terms of a complete end-to-end FCoE solution, there continues to be very little multi-hop FCoE happening, or ports shipping on storage arrays.
In addition, FCoE connections are more prevalent on blade servers than on stand-alone servers for various reasons.
- First, blades are used more in a virtualized environment where different types of traffic can travel on the same link.
- Second, the migration to 10 Gbps has been very slow so far on stand-alone servers; about 80% of these servers are actually still connected with 1 Gbps, which cannot support FCoE.
What portion of FCoE-enabled server ports are actually running storage traffic?
FCoE-enabled ports comprise about a third of total 10 Gbps controller and adapter ports shipped on servers. However, we would like to bring to readers’ attention the wide difference between the portion of 10 Gbps ports that is FCoE-enabled and the portion that is actually running storage traffic. We currently believe less than a third of the FCoE-enabled ports are being used to carry storage traffic. That’s because the FCoE port, in many cases, is provided by default with the server. That’s the case with HP blade servers as well as Cisco’s UCS servers, which together are responsible for around 80% of the FCoE-enabled ports. We believe, however, that in the event that users buy separate adapters they will most likely use that adapter to run storage traffic—but they will need to pay an additional premium for this – about 50% to 100% – for the FCoE license.
That said, whether FCoE-enabled ports are used to carry storage traffic or not, we believe they are being introduced at the expense of some FC adapters. If users deploy a server with an FCoE-enabled port, they most likely will not buy a FC adapter to carry storage traffic. Additionally, as Ethernet speeds reach 40 Gbps, the differential over FC will be too great and FC will be less likely to keep pace.
About the Authors
Casey Quillin is a Senior Analyst, Storage Area Network & Data Center Appliance Market Research with the Dell’Oro Group
Sameh Boujelbene is a Senior Analyst, Server and Controller & Adapter Market Research with the Dell’Oro Group
Our VN2VN Webcast last week was extremely well received. The audience was big and highly engaged. Here is a summary of the questions attendees asked and answers from my colleague, Joe White, and me. If you missed the Webcast, it’s now available on demand.
We are an extremely large FC shop with well over 50K native FC ports. We are looking to bridge this to the FCoE environment for the future. What does VN2VN buy the larger company? Seems like SMB is a much better target for this.
Answer #1: It’s true that for large port count SAN deployments VN2VN is not the best choice but the split is not strictly along the SMB/large enterprise lines. Many enterprises have multiple smaller special purpose SANs or satellite sites with small SANs and VN2VN can be a good choice for those parts of a large enterprise. Also, VN2VN can be used in conjunction with VN2VF to provide high-performance local storage, as we described in the webcast.
Question #2: Are there products available today that incorporate VN2VN in switches and storage targets?
Answer #2: Yes. A major storage vendor announced support for VN2VN at Interop Las Vegas 2013. As for switches, any switch supporting Data Center Bridging (DCB) will work. Most, if not all, new datacenter switches support DCB today. Recommended also is support in the switch for FIP Snooping, which is also available today.
Question #3: If we have an iSNS kind of service for VN2VN, do you think VN2VN can scale beyond the current anticipated limit?
Answer #3: That is certainly possible. This sort of central service does not exist today for VN2VN and is not part of the T11 specifications so we are talking in principle here. If you follow SDN (Software Defined Networking) ideas and thinking then having each endpoint configured through interaction with a central service would allow for very large potential scaling. Now the size and bandwidth of the L2 (local Ethernet) domain may restrict you, but fabric and distributed switch implementations with large flat L2 can remove that limitation as well.
Question #4: Since VN2VN uses different FIP messages to do login, a unique FSB implementation must be provided to install ACLs. Have any switch vendors announced support for a VN2VN FSB?
Answer #4: Yes, VN2VN FIP Snooping bridges will exist. It only requires a small addition to the filet/ACL rules on the FSB Ethernet switch to cover VN2VN. Small software changes are needed to cover the slightly different information, but the same logic and interfaces within the switch can be used, and the way the ACLs are programmed are the same.
Question #5: Broadcasts are a classic limiter in Layer 2 Ethernet scalability. VN2VN control is very broadcast intensive, on the default or control plane VLAN. What is the scale of a data center (or at least data center fault containment domain) in which VN2VN would be reliably usable, even assuming an arbitrarily large number of data plane VLANs? Is there a way to isolate the control plane broadcast traffic on a hierarchy of VLANs as well?
Answer #5: VLANs are an integral part of VN2VN within the T11 FC-BB-6 specification. You can configure the endpoints (servers and storage) to do all discovery on a particular VLAN or set of VLANs. You can use VLAN discovery for some endpoints (mostly envisioned as servers) to learn the VLANs on which to do discovery from other endpoints (mostly envisioned as storage). The use of VLANs in this manner will contain the FIP broadcasts to the FCoE dedicated VLANs. VN2VN is envisioned initially as enabling small to medium SANs of about a couple hundred ports although in principle the addressing combined with login controls allows for much larger scaling.
Question #6: Please explain difference between VN2VN and VN2VF
Answer #6: The currently deployed version of FCoE, T11 FC-BB-5, requires that every endpoint, or Enode in FC-speak, connect with the “fabric,” a Fibre Channel Forwarder (FCF) more specifically. That’s VN2VF. What FC-BB-6 adds is the capability for an endpoint to connect directly to other endpoints without an FCF between them. That’s VN2VN.
Question #7: In the context of VN2VN, do you think it places a stronger demand for QCN to be implemented by storage devices now that they are directly (logically) connected end-to-end?
Answer #7: The QCN story is the same for VN2VN, VN2VF, I/O consolidation using an NPIV FCoE-FC gateway, and even high-rate iSCSI. Once the discovery completes and sessions (FLOGI + PLOGI/PRLI) are setup, we are dealing with the inherent traffic pattern of the applications and storage.
Question #8: Your analogy that VN2VN is like private loop is interesting. But it does make VN2VN sound like a backward step – people stopped deploying AL tech years ago (for good reasons of scalability etc.). So isn’t this just a way for vendors to save development effort on writing a full FCF for FCoE switches?
Answer #8: This is a logical private loop with a lossless packet switched network for connectivity. The biggest issue in the past with private or public loop was sharing a single fiber across many devices. The bandwidth demands and latency demands were just too intense for loop to keep up. The idea of many devices addressed in a local manner was actually fairly attractive to some deployments.
Question #9: What is the sweet spot for VN2VN deployment, considering iSCSI allows direct initiator and target connections, and most networks are IP-enabled?
Answer #9: The sweet spot if VN2VN FCoE is SMB or dedicated SAN deployments where FC-like flow control and data flow are needed for up to a couple hundred ports. You could implement using iSCSI with PFC flow control but if TCP/IP is not needed due to PFC lossless priorities — why pay the TCP/IP processing overhead? In addition the FC encapsulation/serializaition and FC exchange protocols and models are preserved if this is important or useful to the applications. The configuration and operations of a local SAN using the two models is comparable.
Question #10: Has iSCSI become irrelevant?
Answer #10: Not at all. iSCSI serves a slightly different purpose from FCoE (including VN2VN). iSCSI allows connection across any IP network, and due to TCP/IP you have an end-to-end lossless in-order delivery of data. The drawback is that for high loss rates, burst drops, heavy congestion the TCP/IP performance will suffer due to congestion avoidance and retransmission timeouts (‘slow starts’). So the choice really depends on the data flow characteristics you are looking for and there is not a one size fits all answer.
Question #11: Where can I watch this Webcast?
Answer #11: The Webcast is available on demand on the SNIA website here.
Question #12: Can I get a copy of these slides?
Answer #12: Yes, the slides are available on the SNIA website here.
The completion of a specification for FCoE (T11 FC-BB-5, 2009) held great promise for unifying storage and LAN over a unified Ethernet network, and now we are seeing the benefits. With FCoE, Fibre Channel protocol frames are encapsulated in Ethernet packets. To achieve the high reliability and “lossless” characteristics of Fibre Channel, Ethernet itself has been enhanced by a series of IEEE 802.1 specifications collectively known as Data Center Bridging (DCB). DCB is now widely supported in enterprise-class Ethernet switches. Several major switch vendors also support the capability known as Fibre Channel Forwarding (FCF) which can de-encapsulate /encapsulate the Fibre Channel protocol frames to allow, among other things, the support of legacy Fibre Channel SANs from a FCoE host.
The benefits of unifying your network with FCoE can be significant, in the range of 20-50% total cost of ownership depending on the details of the deployment. This is significant enough to start the ramp of FCoE, as SAN administrators have seen the benefits and successful Proof of Concepts have shown reliability and delivered performance. However, the economic benefits of FCoE can be even greater than that. And that’s where VN2VN — as defined in the final draft T11 FC-BB-6 specification — comes in. This spec completed final balloting in January 2013 and is expected to be published this year. The code has been incorporated in the Open FCoE code (www.open-fcoe.org). VN2VN was demonstrated at the Fall 2012 Intel Developer Forum in two demos by Intel and Juniper Networks, respectively.
“VN2VN” refers to Virtual N_Port to Virtual N_Port in T11-speak. But the concept is simply “Ethernet Only” FCoE. It allows discovery and communication between peer FCoE nodes without the existence or dependency of a legacy FCoE SAN fabric (FCF). The Fibre Channel protocol frames remain encapsulated in Ethernet packets from host to storage target and storage target to host. The only switch requirement for functionality is support for DCB. FCF-capable switches and their associated licensing fees are expensive. A VN2VN deployment of FCoE could save 50-70% relative to the cost of an equivalent Fibre Channel storage network. It’s these compelling potential cost savings that make VN2VN interesting. VN2VN could significantly accelerate the ramp of FCoE. SAN admins are famously conservative, but cost savings this large are hard to ignore.
An optional feature of FCoE is security support through Fibre Channel over Ethernet (FCoE) Initialization Protocol (FIP) snooping. FIP snooping, a switch function, can establish firewall filters that prevent unauthorized network access by unknown or unexpected virtual N_Ports transmitting FCoE traffic. In BB-5 FCoE, this requires FCF capabilities in the switch. Another benefit of VN2VN is that it can provide the security of FIP snooping, again without the requirement of an FCF.
Technically what VN2VN brings to the party is new T-11 FIP discovery process that enables two peer FCoE nodes, say host and storage target, to discover each other and establish a virtual link. As part of this new process of discovery they work cooperatively to determine unique FC_IDs for each other. This is in contrast to the BB-5 method where nodes need to discover and login to an FCF to be assigned FC_IDs. A VN2VN node can login to a peer node and establish a logical point-to-point link with standard fabric login (FLOGI) and port login (PLOGI) exchanges.
VN2VN also has the potential to bring the power of Fibre Channel protocols to new deployment models, most exciting, disaggregated storage. With VN2VN, a rack of diskless servers could access a shared storage target with very high efficiency and reliability. Think of this as “L2 DAS,” the immediacy of Direct Attached Storage over an L2 Ethernet network. But storage is disaggregated from the servers and can be managed and serviced on a much more scalable model. The future of VN2VN is bright.