Confusing Mellanox Windows PerfMon Counters


So you start out doing SMB Direct. Maybe you’re doing RoCE, if so there’s a good chance you’ll be using the excellent Mellanox cards. You studied hard, read a lot and put some real effort into setting it up. The SMB Direct / DCB configuration is how you think it should be and things are working as expected.

Curious as you are you want to find out if you can see Priority Flow Control work. Well, the easiest way to do so is by using the Windows Performance Monitor counters that Mellanox provides.

Confusing Mellanox Windows PerfMon Counters

So you take your first look at the Mellanox Adaptor QoS Perfmon counters for ConnectX series for SMB Direct (RDMA) traffic. When you want to see what’s happening in regards to pause frames that have been sent and received and what pause duration was requested from the receiving hop (or received from the sending hop) you can get confused. The naming is a bit counter intuitive.


The Rcv Pause duration is not the duration requested by the pause frames the host received, but by the pause frames that host sent. Likewise, the Sent Pause duration is not the duration requested by the pause frames the host send, but by the pause frames that host received.


So you might end up wondering why your host sends pause frames but to only see the Rcv Pause duration go up. Now you know why Smile.

Now there were plans to fix this in WinOF 4.95. The original release note made mention of this and this made me quite happy as most people are confused enough when it comes to RDMA/RoCE/DCB configurations as it is.

A screenshot of the change in the original Mellanox WinOF VPI Release Notes revision 4.95


Unfortunately, this did not happen. It was removed in a newer version of these release notes. My guess is it could have been a breaking chance of some sort if a lot of tooling or automation is expecting these counter names.

I still remember how puzzled I looked at the counters which to me didn’t make sense and the tedious labor of empirical testing to figure out that the wording was a bit “less than optimal”.

But look, once you know this you just need to keep it in mind. For now, we’ll have to live with some confusing Mellanox Windows PerfMon counter names. At least I hope I have saved you the confusion and time I went through when first starting with these Mellanox counters. Other than that I can only say that you should not be discouraged as they have been and are a great tool in checking RoCE DCB/PFC configs.

RDMA/RoCE & Windows Server 2016 TPv4 Testing


My good buddy and fellow MVP Aidan Finn has promoted disabling advanced features by default in order to avoid downtime for a long time and with good reason. I agree with the fact that too many implementations of features such as UNMAP, ODX, VMQ are causing us issues. This has to improve and meanwhile something has to be done to avoid the blast & fallout of such issues. In this trend Windows Server 2016 is taking steps towards disabling capabilities by default.

Windows 2016 & RDMA/RoCE

In Windows 2012 (R2), RDMA was enabled by default on ConnectX-3 adapters. This is great when you’ve provisioned a lossless fabric for them to use and configure the hosts correctly. As you know by now RoCE requires DCB Priority flow control and optionally ETS to deliver stellar performance.

If SMB 3 detects that RDMA cannot work properly it will fall back top TCP (that’s what that little TCP “standby” connection is for in those SMB Multichannel/Direct drawings. Not working correctly can mean that and RoCE/RDMA connection cannot be establish or fails under load.

To make sure that people get the behavior they desire and not run into issues the idea is to move to have RDMA disabled by default in Windows Server 2016 when DCB/PFC is disabled. At least for the inbox drivers. This is mentioned in RDMARoCE Considerations for Windows 2016 on ConnectX-3 Adapters. When you want it you’ll have to enable it on purpose meaning that they assume you’ve also set up a lossless Ethernet fabric and configured your hosts.

If you don’t want this there is a way to return to the old behavior and that’s a registry key called “NDKWithGlobalPause”. When this key is set to “1” you are basically forcing the NIC to work with Global Pause. Nice for a lab, but not for real world production with RDMA. We want it to be 0, which is the default.


My Lab Experience

Now setting this parameter to 1 for testing on the Mellanox drivers (NOT inbox) in a running lab server it caused a very nice blue screen. Now granted, I’m playing with the 5.10 drivers which are normally not meant for Windows 2016 TPv4. I’m still trying to understand the use & effects of this setting but for now I’m not getting far.


This does not happen on Windows 2012 R2 by the way. I should be using the for Windows 2016 TPv4 testing, even if that one still says TPv3. This beta driver enables:

  • NDKPI 2.0
  • RoCE over SR-IOV
  • Virtualization and RoCE/SMB-Direct on the same port
  • VXLAN Hardware offload
  • PacketDirect


In an ideal world all these advanced features would be enabled out of the box to be used when available and beneficial. Unfortunately, this idea has not worked out well in the real world. Bugs in operating systems, features, NIC firmware and drivers, in storage array firmware and software as well as in switch firmware have made for too many issues for too many people.

There is a push to disable them all by default. The reason for this clear. Avoid down time, data corruption etc. While I can understand this and agree with the practice to avoid issues and downtime it’s also a bit sad.  I do hope that work is being done to make sure that these performance and scalability features become truly reliable and that we don’t end up disabling them all, never to turn them on again. That would mean we’re back to banking on pure raw power or growth for performance & efficiency gains. What does that mean for the big convergence push? If we can’t get these capabilities to be reliable enough for use “as is” now, how much riskier will it become when they are all stacked on top of each other in a converged setup? I’m not to stoked about having ODX, UNMAP, VMQ, RMDA etc. turned off as a “solution” however. I want them to work well and not lose them as a “fix”, that’s unacceptable. When I do turn them on and configure the environment correctly I want them to work well. This industry has some serious work to do in getting there. All this talk of software defined anything will not go far outside of cloud providers if we remain at the mercy of firmware and drivers. In that respect I have seen many software defined solutions get a reality check as early implementations are often a step back in functionality, reliability and capability. It’s very much still a journey. The vision is great, the promise is tempting, but in a production environment I tend to be conservative until I have proven myself it works for us.

Musings On Switch Embedded Teaming, SMB Direct and QoS in Windows Server 2016 Hyper-V

When you have been reading up on what’s new in Windows Server 2016 Hyper-V networking you probably read about Switch Embedded Teaming (SET). Basically this takes the concept of teaming and has this done by the vSwitch. Which means you don’t have to team at the host level. The big benefit that this opens up is the RDMA can be leveraged on vNICs. With host based teaming the RDMA capabilities of your NICs are no longer exposed, i.e. you can’t leverage RDMA. Now this has become possible and that’s pretty big.


With the rise of 10, 25, 40, 50 and 100 Gbps NICs and switches the lure to go fully converged becomes even louder. Given the fact that we now don’t lose RDMA capabilities to the vNICs exposed to the host that call sounds only louder to many.  But wait, there’s even more to lure us to a fully converged solution, the fact that we now do no longer lose RSS on those vNICs! All good news.

I have written an entire whitepaper on convergence and it benefits, drawback, risks & rewards. I will not repeat all that here. One point I need to make that lossless traffic and QoS are paramount to the success of fully converged networking. After all we don’t want lossy storage traffic and we need to assure adequate bandwidth for all our types of traffic. For now, in Technical Preview 3 we have support for Software Defined Networking (SDN) QoS.

What does that mean in regards to what we already use today? There is no support for native QoS  and vSwitch QoS in Windows Server 2016 TPv3. There is however the  mention of DCB (PFC/ETS ), which is hardware QoS in the TechNet docs on Remote Direct Memory Access (RDMA) and Switch Embedded Teaming (SET). Cool!

But wait a minute. When we look at all kinds of traffic in a converged Hyper-V environment we see CSV (storage traffic), live migration (all variations), backups over SMB3 all potentially leveraging SMB Direct. Due to the features and capabilities in SMB3 I like that. Don’t get me wrong about that. But it also worries me a bit when it comes to handling QoS on the hardware side of things.

In DCB Priority Flow Control (PFC) is the lossless part, Enhanced Transmission Selection (ETS) is the minimum bandwidth QoS part. But how do we leverage ETS when all types of traffic use SMB Direct. On the host it all gets tagged with the same priority. ETS works by tagging different priorities to different workloads and assuring minimal bandwidths out of a total of 100% without reserving it for a workload if it doesn’t need it. Here’s a blog post on ETS with a demo video DCB ETS Demo with SMB Direct over RoCE (RDMA .

Does this mean a SDN QoS only approach to deal with the various type of SMB Direct traffic or do they have some aces up their sleeves?

This isn’t a new “concern” I have but with SET and the sustained push for convergence it does has the potential to become an issue. We already have the SMB bandwidth limitation feature for live migration. That what is used to prevent LM starving CSV traffic when needed. See Preventing Live Migration Over SMB Starving CSV Traffic in Windows Server 2012 R2 with Set-SmbBandwidthLimit.

Now in real life I have rarely, if ever, seen a hard need for this. But it’s there to make sure you have something when needed. It hasn’t caused me issues yet, but I’m a performance & scale first, in “a non-economies of scale” world compared to hosters. As such convergence is a tool I use with moderation. My testing when traffic competes without ETS is that they all get part of the cake but not super predictable/ consistent. SMB bandwidth limitation is a bit of a “bolted on” solution => you can see the perf counters push down the bandwidth in an epic struggle to contain it, but as said it’s a struggle, not a nice flat line.

Also Set-SmbBandwidthLimit is not a percentage, but hard max bandwidth limit, so when you lose a SET member the math is off and you could be in trouble fast. Perhaps it’s these categories that could or will be used but it doesn’t seem like the most elegant solution/approach. That with ever more traffic leveraging SMB Direct make me ever more curious. Some switches offer up to 4 lossless queues now so perhaps that’s the way to go leveraging more priorities … Interesting stuff! My preferred and easiest QoS tool, get even bigger pipes, is an approach convergence and evolution of network needs keeps pushing over. Anyway, I’ll be very interested to see how this is dealt with. For now I’ll conclude my musings On Switch Embedded Teaming, SMB Direct and QoS in Windows Server 2016 Hyper-V

High performance live migration done right means using SMB Direct

I  saw people team two 10GBps NICs for live migration and use TCP/IP. They leveraged LACP for this as per my blog Teamed NIC Live Migrations Between Two Hosts In Windows Server 2012 Do Use All Members . That was a nice post but not a commercial to use it. It was to prove a point that LACP/Static switch dependent teaming did allow for multiple VMs to be live migrated in the same direction between two node. But for speed, max throughput & low CPU usage teaming is not the way to go. This is not needed as you can achieve bandwidth aggregation and redundancy with SMB via Multichannel. This doesn’t require any LACP configuration at all and allows for switch independent aggregation and redundancy. Which is great, as it avoids stacking with switches that don’t do  VLT, MLAG,  …

Even when your team your NICs your better off using SMB. The bandwidth aggregation is often better. But again, you can have that without LACP NIC teaming so why bother? Perhaps one reason, with LACP failover is faster, but that’s of no big concern with live migration.

We’ll do some simple examples to show you why these choices matter. We’ll also demonstrate the importance of an optimize RSS configuration. Do not that the configuration we use here is not a production environment, it’s just a demo to show case results.

But there is yet another benefit to SMB.  SMB Direct.  That provides for maximum throughput, low latency and low CPU usage.

LACP NIC TEAM with 2*10Gbps with TCP

With RSS setting on the inbox default we have problems reaching the best possible throughput (17Gbps). But that’s not all. Look at the CPU at the time of live migration. As you can see it’s pretty taxing on the system at 22%.


If we optimize RSS with 8 RSS queues assigned to 8 physical cores per NIC on a different CPU (dual socket, 8 core system) we sometimes get better CPU overhead at +/- 12% but the throughput does not improve much and it’s not very consistent. It can get worse and look more like the above.


LACP NIC TEAM with 2*10Gbps with SMB (Multichannel)

With the default RSS Settings we still have problems reaching the best possible throughput but it’s better (19Gbps). CPU wise, it’s pretty taxing on the system at 24%.


If we optimize RSS with 8 RSS queues assigned to 8 physical cores per NIC on a different CPU (dual socket, 8 core system) we get better over CPU overhead at +/- 8% but the throughput actually declined (17.5 %). When we run the test again we were back to the results we saw with default RSS settings.


Is there any value in using SMB over TCP with LACP for live migration?

Yes there is. Below you see two VMs live migrate, RSS is optimized. One core per VM is used and the throughput isn’t great, is it. Depending on the speed of your CPU you get at best 4.5 to 5Gbps throughput per VM as that 1 core per VM is the limiting factor. Hence see about 9Gbps here, as there’s 2 VMs, each leveraging 1 core.


Now look at only one VM with RSS is optimized with SMB over an LACP NIC team. Even 1 large memory VM leverages 8 cores and achieves 19Gbps.


What about Switch Independent Teaming?

Ah well that consumes a lot less CPU cycles but it comes at the price of speed. It has less CPU overhead to deal with in regards to LACP. It can only receive on one team member. The good news is that even a single VM can achieve 10Gbps (better than LACP) at lower CPU overhead. With SMB you get better CPU distribution results but as the one member is a bottle neck, not faster. But … why bother when we have …better options!? Read on Smile!

No Teaming – 2*10Gbps with SMB Multichannel, RSS Optimized

We are reaching very good throughput but it’s better (20Gbps) with 8 RSS queues assigned to 8 physical cores. The CPU at the time of live migration is pretty good at 6%-7%.


Important: This is what you want to use if you don’t have 10Gbps but you do have 4* 1Gbps NICs for live migration. You can test with compression and LACP teaming if you want/can to see if you get better results. Your mirage may vary Smile. If you have only one 1Gbps NIC => Compression is your sole & only savior.

2*10Gbps with SMB Direct

We’re using perfmon here to see the used bandwidth as RDMA traffic does not show up in Task Manager.


We have no problems reaching the best possible throughput but it’s better (20Gbps, line speed). But now look at the CPU during live migration. How do you like them numbers?

Do not buy non RDMA capable NICs or Switches without DCB support!

These are real numbers, the only thing is that the type and quality of the NICs, firmware and drivers used also play a role an can skew the results a bit. The onboard LOM run of the mill NICs aren’t always the best choice. Do note that configuration matters as you have seen. But SMB Direct eats them all for breakfast, no matter what.

Convinced yet? People, one of my core highly valuable skillsets is getting commodity hardware to perform and I tend to give solid advice. You can read all my tips for fast live migrations here in Live Migration Speed Check List – Take It Easy To Speed It Up

Does all of this matter to you? I say yes , it does. It depends on your environment and usage patterns. Maybe you’re totally over provisioned and run only very small workloads in your virtual machines. But it’s save to say that if you want to use your hardware to its full potential under most circumstances you really want to leverage SMB Direct for live migrations. What about that Hyper-V cluster with compute and storage heavy applications, what about SQL Server virtualization? Would you not like to see this picture with SMB RDMA? The Mellanox  RDMA cards are very good value for money. Great 10Gbps switches that support DCB (for PFC/ETS) can be bought a decent prices. You’re missing out and potentially making a huge mistake not leveraging SMB Direct for live migrations and many other workloads. Invest and design your solutions wisely!