NVM Express over Fabrics


Any technologist who’s read, let alone used NVM Express (NVMe), is pretty enthusiastic about it’s capabilities and if it was not for availability and financial restrictions we’d all have at least a couple in our home systems and labs. It seems to succeed very well in making sure the host can keep up with the performance (low latencies, high throughput)) delivered by SSD drives than our current interfaces.

This means that many are very happy with future visions on how PCIe will dislodge SAS/SATA as the preferred SSD interface. This might seem feasible for local storage right now but how to deal with this in an actual storage array, what if we want to size this to a larger scale? There are no “PCIe JBODS”. So what does one do? Well, how did we do it in the past with FC? We created a fabric. Below we see several local & remote NVMe architectures even hybrid ones with traditional SAS.

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That’s exactly what NVM Express Inc. is doing, creating the specs for a fabric. This holds the promise to achieve superior results due to the elimination of SCSI translation which reduces latency significantly by delivering NVMe end to end. Not only that but we also see the following efforts in the NVM Express Specification 1.2 to give it enterprise grade capabilities beyond pure performance.

  • Enhanced status reporting
  • Expanded capabilities including live firmware updates

There have been some early demos of NVMe over Fabrics mainly focusing on the “remote” performance. While local NVMe SSDs have the edge on absolute IOPS the difference with NVMe over a fabric is not significant. The reduction in latency is measured in < 10 µs,so that’s good news. The fabric leverages RDMA (yes, yet another reason that my time spending with this technology has been a useful investment). This can be Infiniband, RoCE or iWarp. There’s also the new kid on the block “Intel Omni Scale”  (even if their early demo used iWARP). There’s also a Mellanox RoCE demo.

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Now with NVMe SSD disk speeds it seems that the writing is on the wall that ever better fabric performance will be needed to support the tremendous throughput this evolution of storage can deliver. RDMA seems poised for success in regards to this. Now, yes, strictly speaking the NVMe traffic does not require RDMA but let’s just say I don’t see anyone building it without. I also think this means even iWarp fabrics will use DCB (PFC) to make sure we have a lossless network. The amount of traffics will be immense and why not optimize for the best possible performance? I hold the opinion this is beneficial for east-west traffic today in larger environments, especially when in converged networks. Unless the Intel® Omni-Path Architecture blows everyone else away that is Smile. Too early to tell.

Now does this dictate the total and absolute obsolescence of iSCSI and FC? No. There is no reason why a NVMe Fabrics storage solution cannot offer storage to hosts via FC, iSCSI, SMB 3, NFS, FCoE, … They, potentially could even offer iWarp, RoCE or Infiniband to the hosts so you won’t lose your prior investments or get locked into one. I have no magic ball so I cannot tell you if this will happen. What I do now that when it comes to MPIO versus multichannel for load balancing and even failover and recovery, multichannel sometimes does a (far?) superior job in my honest opinion especially with older hypervisors even when the hypervisor uses separate sessions per virtual machine to achieve better load balancing over iSCSI or the like. Anyway, I digress. One thing I do know is that I’ll keep a keen eye on what Microsoft is doing in this space, especially in regards to Windows Server 2016. It’s time to up the level on scalability & support for newer technologies once again.

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SMB Direct: Choosing A Flavor


I often get asked what to buy for implementing SMB Direct. It’s a non trivial question actually and I’m not an expert, nor do I play one on TV.  All joking aside, it’s a classical consulting answer: it depends. I don’t do free consulting in a blog post, even if that was possible, as there are many factors such as the characteristics and futures of your organization. There’s also a lot of FUD & marketing flying around. Basically in real life you only have two vendors: Cheslio (iWarp) and Mellanox (Roce/Infiniband). Hard to say which one is best. You make the best choice for your company and you live with it.

There is talk about other vendors joining the SMB Direct market. But it seems to be taking a while. This is not that strange. I’ve understood that in the early days of this century iWarp got a pretty bad reputation due to the many issues around it. Apparently offloading the TCP/IP stack to the NIC, which is what iWarp does is not an easy endeavor. Intel had some old Net card a couple of years ago but has gotten out of the game. Perhaps they’ll step back in but that might very well take a couple of years.

Other vendors like Broadcom, Emulex & QLogic might be working on solutions but I’m not holding my breath. Broadcom has DCB and has been hinting at RDMA in it’s NICs for many years but as of the writing of this post there is nothing functional out there yet. But bar the slowness (is complexity slowing the process?) it will be very interesting to see what they’ll choose: RoCE or iWarp. That choice might be the most public statement we’ll ever see about what technology seems like the best bet for these companies. But be careful, I have seen technology choices based on working/living with design choices at at another level due to constrictions in hardware & software that are no longer true today. So don’t just do blindly what others do.

Infiniband will remain a bit more of a niche I think and my guess is that RoCE is the big bet of Mellanox for the long term. 10Gbps and higher Ethernet switches are sold to everyone in the world. Infiniband, not so much. Does that make it a bad choice? Nope, it all depends. Just like FC is not a bad choice for everyone today, it depends.

Your options today

The options you have today to do SMB Direct are rather limited and bound to the different flavors and their vendor. Yes vendor not vendors.

  1. iWarp: Chelsio
  2. RoCE: Mellanox (v2 of RoCE has brought routability into the game, which counters one of iWarps biggest advantages, next to operational ease but the no fuss about DCB story might not be 100% correct, the question is if this matters, after all many people do well with iSCSI which is easy but has performance limits).
  3. Infiniband: Mellanox (Qlogic was the only other remaining one, but Intel bought it form them. I have never ever seen Intel Infiniband in the wild.

Note: You can do iWarp (and even RoCE in theory) without DCB but in all realistic high traffic situations you’ll want to implement PFC to keep the experience and results good under load. Especially the ports connecting to the SOFS nodes could other wise potentially drop packets. iWarp, being TCP/IP, will handle dropped packets but possibly at the cost of deteriorated performance. With RoCE you’re basically toast if you lose packets, it should be losses. I’m not too convinced that pure offloaded TCP/IP scales. Let’s face it, what was the big deal about lossless iSCSI => DCB Smile I would really love to see Demartek testing these things out for us.

If you have a smaller environment, no need for routing and minimal politics I have seen companies select Infiniband which per Gbps is very cheap. Lots of people have chosen iWarp due to it simplicity (which they heavily market) and routability. The popularity however has dropped due to prices hikes that came with increased demand and no competition. RoCE  is popular (I see it the most) and affordable but for this one you MUST do at least PFC. DCB support on switches is not an issue, even budget friendly DELL PowerConnect N4000 series supports it as did it’s predecessor the PC8100 series. Meaning if you have bought switches in the past 24 months and did your home work you’re good to go. Are routability and distance important? Well perhaps not that much today but as the trend in networking is heading for layer 3 down to the rack which will be more acceptable when we see a lot of the workload goodness in hypervisors (Live Migration, vMotion,yes there is work being done on that) being lit up in layer 3 it might become a key feature.

Complete VM Mobility Across The Data Center with SMB 3.0, RDMA, Multichannel & Windows Server 2012 (R2)


Introduction

The moment I figured out that Storage Live Migration (in certain scenarios) and Shared Nothing Live Migration leverage SMB 3.0 and as such Multichannel and RDMA in Windows Server 2012 I was hooked. I just couldn’t let go of the concept of leveraging RDMA for those scenarios.  Let me show you the value of my current favorite network design for some demanding Hyper-V environments. I was challenged a couple of time on the cost/port of this design which is, when you really think of it, a very myopic way of calculating TCO/ROI. Really it is. And this week at TechEd North America 2013 Microsoft announced that all types of Live Migrations support Multichannel & RDMA (next to compression) in Windows Server 2012 R2.  Watch that in action at minute 39 over here at Understanding the Hyper-V over SMB Scenario, Configurations, and End-to-End Performance. You should have seen the smile on my face when I heard that one! Yes standard Live Migration now uses multiple NIC (no teaming) and RDMA for lightning fast  VM mobility & storage traffic. People you will hit the speed boundaries of DDR3 memory with this! The TCO/ROI of our plans just became even better, just watch the session.

So why might I use more than two 10Gbps NIC ports in a team with converged networking for Hyper-V in Windows 2012? It’s a great solution for sure and a combined bandwidth of 2*10Gbps is more than what a lot of people have right now and it can handle a serious workload. So don’t get me wrong, I like that solution. But sometimes more is asked and warranted depending on your environment.

The reason for this is shown in the picture below. Today there is no more limit on the VM mobility within a data center. This will only become more common in the future.

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This is not just a wet dream of virtualization engineers, it serves some very real needs. Of cause it does. Otherwise I would not spend the money. It consumes extra 10Gbps ports on the network switches that need to be redundant as well and you need to have 10Gbps RDMA capable cards and DCB capable switches.  So why this investment? Well I’m designing for very flexible and dynamic environments that have certain demands laid down by the business. Let’s have a look at those.

The Road to Continuous Availability

All maintenance operations, troubleshooting and even upgraded/migrations should be done with minimal impact to the business. This means that we need to build for high to continuous availability where practical and make sure performance doesn’t suffer too much, not noticeably anyway. That’s where the capability to live migrate virtual machines of a host, clustered or not, rapidly and efficiently with a minimal impact to the workload on the hosts involved comes into play.

Dynamics Environments won’t tolerate downtime

We also want to leverage our resources where and when they are needed the most. And the infrastructure for the above can also be leveraged for that. Storage live migration and even Shared Nothing Live Migration can be used to place virtual machine workloads where they are getting the resources they need. You could see this as (dynamically) optimizing the workload both within and across clusters or amongst standalone Hyper-V nodes. This could be to a SSD only storage array or a smaller but very powerful node or cluster in regards to CPU, memory and Disk IO. This can be useful in those scenarios where scientific applications, number crunching or IOPS intesive  software or the like needs them but only for certain times and not permanently.

Future proofing for future storage designs

Maybe you’re an old time fiber channel user or iSCSI rules your current data center and Windows Server 2012 has not changed that. But that doesn’t mean it will not come. The option of using a Scale Out File Server and leverage SMB 3.0 file shares to providing storage for Hyper-V deployments is a very attractive one in many aspects. And if you build the network as I’m doing you’re ready to switch to SMB 3.0 without missing a heart beat. If you were to deplete the bandwidth x number of 10Gbps can offer, no worries you’ll either use 40Gbps and up or Infiniband. If you don’t want to go there … well since you just dumped iSCSI or FC you have room for some more 10Gbps ports Smile

Future proofing performance demands

Solutions tend to stay in place longer than envisioned and if you need some long levity and a stable, standard way of doing networking, here it is. It’s not the most economical way of doing things but it’s not as cost prohibitive as you think. Recently I was confronted again with some of the insanities of enterprise IT. A couple of network architects costing a hefty daily rate stated that 1Gbps is only for the data center and not the desktop while even arguing about the cost of some fiber cable versus RJ45 (CAT5E). Well let’s look beyond the North – South traffic and the cost of aggregating band all the way up the stack with shall we? Let me tell you that the money spent on such advisers can buy you in 10Gbps capabilities in the server room or data center (and some 1Gbps for the desktops to go) if you shop around and negotiate well. This one size fits all and the ridiculous economies of scale “to make it affordable” argument in big central IT are not always the best fit in helping the customers. Think  a little bit outside of the box please and don’t say no out of habit or laziness!

Conclusion

In some future blog post(s) we’ll take a look at what such a network design might look like and why. There is no one size fits all but there are not to many permutations either. In our latest efforts we had been specifically looking into making sure that a single rack failure would not bring down a cluster. So when thinking of the rack as a failure domain we need to spread the cluster nodes across multiple racks in different rows. That means we need the network to provide the connectivity & capability to support this, but more on that later.