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    Questions on the 2017 Ethernet Roadmap for Networked Storage

    January 9th, 2017

    Last month, experts from Dell EMC, Intel, Mellanox and Microsoft convened to take a look ahead at what’s in store for Ethernet Networked Storage this year. It was a fascinating discussion of anticipated updates. If you missed the webcast, “2017 Ethernet Roadmap for Networked Storage,” it’s now available on-demand. We had a lot of great questions during the live event and we ran out of time to address them all, so here are answers from our speakers.

    Q. What’s the future of twisted pair cable? What is the new speed being developed with twisted pair cable?

    A. By twisted pair I assume you mean USTP CAT5,6,7 etc.  The problem going forward with high speed signaling is the USTP stands for Un-Shielded and the signal radiates off the wire very quickly.   At 25G and 50G this is a real problem and forces the line card end to have a big, power consuming and costly chip to dig the signal out of the noise. Anything can be done, but at what cost.  25G BASE-T is being developed but the reach is somewhere around 30 meters.  Cost, size, power consumption are all going up and reach going down – all opposite to the trends in modern high speed data centers.  BASE-T will always have a place for those applications that don’t need the faster rates.

    Q. What do you think of RCx standards and cables?

    A. So far, Amphenol, JAE and Volex are the suppliers who are members of the MSA. Very few companies have announced or discussed RCx.  In addition to a smaller connector, not having an EEPROM eliminates steps in the cable assembly manufacture, hence helping with lowering the cost when compared to traditional DAC cabling. The biggest advantage of RCx is that it can help eliminate bulky breakout cables within a rack since a single RCx4 receptacle can accept a number of combinations of single lane, 2 lane or 4 lane cable with the same connector on the host. RCx ports can be connected to existing QSFP/SFP infrastructure with appropriate cabling. It remains to be seen, however, if it becomes a standard and popular product or remain as a custom solution.

    Q. How long does AOC normally reach, 3m or 30m?  

    A. AOCs pick it up after DAC drops off about 3m.  Most popular reaches are 3,5,and 10m and volume drops rapidly after 15,20,30,50, and100. We are seeing Ethernet connected HDD’s at 2.5GbE x 2 ports, and Ceph touting this solution.  This seems to play well into the 25/50/100GbE standards with the massive parallelism possible.

    Q. How do we scale PCIe lanes to support NVMe drives to scale, and to replace the capacity we see with storage arrays populated completely with HDDs?

    A. With the advent of PCIe Gen 4, the per-lane rate of PCIe is going from 8 GT/s to 16GT/s. Scaling of PCIe is already happening.

    Q. How many NVMe drives does it take to saturate 100GbE?

    A. 3 or 4 depending on individual drives.

    Q. How about the reliability of Ethernet? A lot of people think Fibre Channel has better reliability than Ethernet.

    A. It’s true that Fibre Channel is a lossless protocol. Ethernet frames are sometimes dropped by the switch, however, network storage using TCP has built in error-correction facility. TCP was designed at a time when networks were less robust than today. Ethernet networks these days are far more reliable.

    Q. Do the 2.5GbE and 5GbE refer to the client side Ethernet port or the server Ethernet port?

    A. It can exist on both the client side and the server side Ethernet port.

    Q. Are there any 25GbE or 50GbE NICs available on the market?

    A. Yes, there are many that are on the market from a number of vendors, including Dell, Mellanox, Intel, and a number of others.

    Q. Commonly used Ethernet speeds are either 10GbE or 40GbE. Do the new 25GbE and 50GbE require new switches?

    A. Yes, you need new switches to support 25GbE and 50GbE. This is, in part, because the SerDes rate per lane at 25 and 50GbE is 25Gb/s, which is not supported by the 10 and 40GbE switches with a maximum SerDes rate of 10Gb/s.

    Q. With a certain number of SerDes coming off the switch ASIC, which would you prefer to use 100G or 40G if assuming both are at the same cost?

    A. Certainly 100G. You get 2.5X the bandwidth for the same cost under the assumptions made in the question.

    Q. Are there any 100G/200G/400G switches and modulation available now?

    A. There are many 100G Ethernet switches available on the market today include Dell’s Z9100 and S6100, Mellanox’s SN2700, and a number of others. The 200G and 400G IEEE standards are not complete as of yet. I’m sure all switch vendors will come out with switches supporting those rates in the future.

    Q. What does lambda mean?

    ALambda is the symbol for wavelength.

    Q. Is the 50GbE standard ratified now?

    A. IEEE 802.3 just recently started development of a 50GbE standard based upon a single-lane 50 Gb/s physical layer interface. That standard is probably about 2 years away from ratification. The 25G Ethernet Consortium has a ratified specification for 50GbE based upon a dual-lane 25 Gb/s physical layer interface.

    Q. Are there any parallel options for using 2 or 4 lanes like in 128GFCp?

    A. Many Ethernet specifications are based upon parallel options. 10GBASE-T is based upon 4 twisted-pairs of copper cabling. 100GBASE-SR4 is based upon 4 lanes (8 fibers) of multimode fiber. Even the industry MSA for 100G over CWDM4 is based upon four wavelengths on a duplex single-mode fiber. In some instances, the parallel option is based upon the additional medium (extra wires or fibers) but with fiber optics, parallel can be created by using different wavelengths that don’t interfere with each other.

     

     


    Ethernet Roadmap for Networked Storage Q&A

    July 17th, 2015

    Almost 200 people attended our joint Webcast with the Ethernet Alliance: “The 2015 Ethernet Roadmap for Networked Storage.” We had a lot of great questions during the live event, but we did not have time to answer them all. As promised, we’ve complied answers for all of the questions that came in. If you think of additional questions, please feel free to comment on this blog.

    Q. What did you mean by parity of flash with HDD?

    A. We were referring to the O’Reilly article in “Network Computing.”  O’Reilly is predicting parity in BOTH capacity and price in 2016.

    Q. When do we expect IEEE standards ratification for 25G speed?

    A. 2016.  You can see the exact schedule here.

    Q. Do you envision the Enterprise, Cloud Providers, HPC, Financials getting rid of their 10/40GbE infrastructure and replacing that with 25/100GbE infrastructure in 2017? Will these customers deploy 100GbE/25GbE switch in the leaf layer in 2017?

    A. Deployment will occur over a multi-year time span overall if only because switch infrastructure is expensive to upgrade, as reflected in the Crehan Research forecast.  New deployments will likely move to 25/100GbE as new switches with 100GbE downstream ports become available in 2016.   Just because the Cloud Service Providers are currently the most aggressive in driving new infrastructure purchases, they represent the largest early volumes for 25/100 GbE.  Enterprise is still in the midst of the transition from 1GbE to 10GbE.

    Q. What are some of the developments on spanning-tree derivatives vs. Dykstra based derivatives such as OSPF, FSPF for switches?

    A. Beyond the scope of this presentation on Ethernet.  Ethernet is defined by the IEEE for L1 and L2 in the ISO model.  Your questions are at L3 and L4, which is handled by organizations like IETF.

    Q. With all the speeds possible who is working on flow control?

    A. Flow control at the 802.1 level is supported in the Layer 1/2 PHY & MAC by setting upper bounds on the delay through each layer which allows higher layers to comprehend the delays & response times to pause frames. Each new speed & PHY in 802.3 is accompanied by delay constraint specifications to support this.

    Q.  Do you have an overlay graphic that shows the Ethernet RDMA roadmap?  If so, is Ethernet storage the primary driver for that technology?

    A.  Beyond the scope of this presentation on Ethernet.  Ethernet is defined by the IEEE for L1 and L2 in the ISO model.  Your questions are at L3 and L4, which is handled by organizations like IETF and the InfiniBand Trade Association.

    Q. The adoption of faster and new Ethernet always has to do with the costs of acquiring new technology. How long do you think it will take to adopt/acquire faster Ethernet in datacenters now that the development is happening much faster than the last 20 years?

    A. Please see the chart on slide 7 where Crehan Research predicts how fast the technology will diffuse into deployments.

    Q. What do you expect as cost comparison between Ethernet and InfiniBand going forward?
    Also, what work is being done to reduce latency?

    A. Beyond the scope of this presentation.  Latency is primarily a consequence of design methodologies and semiconductor process technology, and thus under the control of the silicon device manufacturers.  Some vendors prioritize latency more than others.

    Q. What’s the technical limitation as speeds go higher and higher?

    A. A number of factors limit speeds going faster and faster, but the main problem is that materials attenuate signals as they travel at higher frequencies.

    Q. Will 1GbE used for manageability purposes disappear from public cloud? If so, what is the expected time frame?

    A. This is a choice for end users.  Most equipment is managed on a separate network for security concerns, but users can eliminate these management networks at any time.

    Q. What are the relative market size predictions for the expanding number of standards (25G, 50G, 100G, 200G, etc.)?

    A. See the Crehan Research forecast in the presentation.

    Q. What is the major difference between SMF & MMF for the not so initiated?

    A. The SMF has a 9um core while the MMF has a 50um core.  Different lasers are used for each fiber type and MMF typically goes 100 meters above 10GbE and SMF goes from 500m to 10km.

    Q. Will 25G be available through both copper and fibre connectivity?

    A. Yes.  IEEE 802.3 work is currently underway to specify 25Gb/s on twinax (“direct attach copper)” to 5 meters, printed circuit backplane up to ~1m, twisted pair copper to 30m, multimode fiber to 100m.  There is no technology barrier to 25G on SMF, just that a standards project to specify it has not started yet.

    Q. This is interesting from a hardware viewpoint, but has nothing to do with storage yet.  Are we going to get to how this relates to storage other than saying flash drives are fast and only Ethernet can keep up?

    A. Beyond the scope of this presentation on Ethernet.  Ethernet is defined by the IEEE for L1 and L2 in the ISO model.  Your questions are directed at the higher layers.  The key point of this webcast is that storage networking engineers need to pay much more attention to the Ethernet roadmap than they have historically, primarily because of NVM.

    Q. How does “SFP 28″ fit in this mix?  Is it required for 25G?

    A. SFP28 connectors and modules are required for 25GbE because they give better performance than SFP+ that only works to 10GbE.

    Q. Can you provide the quick difference between copper & optical on speed & costs?

    A. Copper and optical Ethernet links are usually standardized at the same speed.  400GbE is not defining a copper link but an active Direct Attached Cable (DAC) will probably support 400GbE.  Cost depends on volume and many factors and is beyond the scope of this presentation.  Copper is usually a fraction of the cost of optical links.

    Q. Do you think people will try to use multiple CAT 5e to get more aggregate bandwidth to the access points to avoid having to run Fibre to them?

    A. IEEE is defining 2.5GBASE-T and 5GBASE-T to enable Cat5e to support faster wireless access points.

    Q. When are higher speeds and PoE going to reach the point when copper based Ethernet will become a viable heat source for buildings thus helping the environment?

    A. :)  IEEE is defining 4 wire PoE to deliver at least 60W to end devices.  You can find out more here.

    Q. What are the use cases for 2.5Gb and 5.0Gb Base-T?

    A. The leading use case for 2.5G/5GBASE-T is to provide the uplink for wireless LAN access points that support 802.11ac and future wireless technology.  Wireless LAN technology has advanced to the point where >1Gb/s BW is needed upstream from the AP, and 2.5G/5G provide a higher speed uplink while preserving the user’s investment in Cat5e/Cat6 cabling.

    Q. Why not have only CFP2 sockets right away with things disabled for lower speeds for all the intervening years leading to full-fledged CFP2?

    A. CFP2 is defined for 100GbE and 8 ports can be used on a 1U switch. 100GbE switches are shifting to QSFP28 so that 32 ports of 100GbE is supported in a 1U switch at low cost.  The CFP2 is much more expensive than QSFP28 and will not be used for lower speeds because of the high cost.