Veeam Backup & Replication Preferred Subnet & SMB Multichannel


In a previous blog post Veeam Backup & Replication leverages SMB Multichannel post we showed that Veeam backup & Replication leverages SMB multichannel when possible.

But what about Veeam Backup & Replication Preferred Subnet & SMB Multichannel, does that work? We mentioned that we wanted to answer the question what happens if we configure a preferred back-up network in Veeam Backup & Replication. Would this affect the operation of SMB multichannel at all? By that I means, would enabling a preferred network in Veeam prevent multichannel from using more than one NIC?

In this blog post we dive in to that question and some scenarios. We actually need to be able to deal with multiple scenarios. When you have equally capable NICs that are on different subnets you might want to make sure it uses only one. Likewise, you want both to be used whether they are or are not on the same subnet even if you set a preferred subnet in Veeam. The good news is that the nature of SMB Multichannel and how Veaam preferred networks work do allow for flexibility to achieve this. But it might not work like you would expect, unless you understand SMB Multichannel.

Veeam Backup & Replication Preferred Subnet & SMB Multichannel

For this blog post we adapt our lab networking a bit so that our non-management 10Gbps rNICs are on different subnets. We have subnet for one set of NICs and for the second set of NICs. This is shown in the figure below.


These networks can live in a separate VLAN or not, that doesn’t really matter. It does matter if to have a tagged VLAN or VLANS if you want to use RDMA because you need it to have the priority set.

We now need to configure our preferred network in Veeam Backup & Replication. We go to the main menu and select Network Traffic Rules


In the Global Network Traffic Rules window, click Networks.


In the Preferred Networks window, select the Prefer the following networks for backup and replication traffic check box.


Click Add. We use the CIDR notation to fill out our preferred network or you can use the network mask and click OK.

To prove a point in regards to how Multichannel works isn’t affected by what you fill out here we add only one of our two subnets here. SMB will see where it can leverage SMB multichannel and it will kick in. Veeam isn’t blocking any of its logic.

So now we kick of a backup of our Hyper-V host to our SMB hare target backup repository. We can see multichannel work just fine.


Below is a screenshot on the backup target of the backup running over SMB multichannel, leveraging 2 subnets, while having set only one of those as the preferred network in Veeam Backup & Replication


Look at my backup fly … and this is only one host that’s being backup (4 VMs actually). Have I told you how much I love flash storage? And why I’m so interested in getting ReFS hybrid volumes with SSD/SATA disks to work as backup target? I bet you do!

Looking good and it’s easy, right? Well not so fast!

Veeam does not control SMB Multichannel

Before you think you’re golden here and in control via Veeam lets do another demo. In the preferred network, we enter a subnet available to both the source and the target server but that is an LBFO (teamed) NIC with to 1Gbps members (RSS is enabled).


No let’s see what happens when we kick of a backup.


Well SMB multichannel just goes through its rules and decided to take the two best, equally capable NICs. These are still our two 10Gbps rNICs. Whatever you put in the preferred network is ignored.

This is neither good or bad but you need to be aware of this in order to arrange for backups to leverage the network path(s) you had in mind. This is to avoid surprises. The way to do that the same as you plan and design for all SMB multichannel traffic.

As stated in the previous blog post you can control what NICs SMB multichannel will use by designing around the NIC capabilities or if needed disabling or enabling some of these or by disabling SMB multichannel on a NIC. This isn’t always possible or can lead to issues for other workloads so the easiest way to go is using SMB Multichannel Constraints. Do note however that you need to take into consideration what other workloads on your server leverage SMB Multichannel when you go that route to avoid possible issues.

As an example, I disabled multichannel on my hosts. Awful idea but it’s to prove point. And still with our subnet set as preferred subnet I ran a backup again.


As you can see the 2*1Gbps LBFO NIC is doing all the lifting on both hosts as it’s switch independent and not LACP load balancing mode we’re limited to 1Gbps.

So how do we control the NICs used with SMB multichannel?

Well SMB Multichannel rules apply. You use your physical design, the capabilities of the NICs and SMB constraints. In reality you’re better off using your design and if needed SMB multichannel constraints to limit SMB to the NICs you want it to use. Do not that disabling SMB Multichannel (client and or server) is a global for the host. Consider this as it affects all NICs on the host, not just the ones you have in mind for your backups. In most cases these NICs will be the same. Messing around with disabling multichannel or NIC capabilities (RSS, RDMA) isn’t a great solution. But it’s good to know the options and behavior.

Some things to note

Realize you don’t even have to set both subnets in the preferred subnets if they are different. SMB kicks of over one, sees it can leverage both and just does so. The only thing you manipulated here SMB multichannel wise is which subnet is used first.

If both of our rNICs would have been on the same subnet you would not even have manipulated this.

Another thing that’s worth pointing out that this doesn’t require your Veeam Backup & Replication VM to have an IP address in any of the SMB multichannel subnets. So as long as the source Hyper-V hosts and the backup target are connected you’re good to go.

Last but not least, and already mentioned in the previous blog post, this also leverages RDMA capabilities when available to help you get the best throughput, lowest latency and leave those CPU cycles for other needs. Scalability baby! No I realize that you might think that the CPU offload benefit is not a huge deal on your Hyper-V host but consider the backup target being hammered by several simultaneous backups. And also consider that some people their virtual machines look like below in regards to CPU usage, in ever more need of more vCPU and CPU time slices.


And that’s what the Hyper-V host looks like during a backup without SMB Direct (with idle VMs mind you).


All I’m saying here is don’t dismiss RDMA too fast, everything you can leverage to help out and that is available for free in the box is worth considering.

Note: I have gotten the feedback that Veeam doesn’t support SMB Direct and that this was confirmed by Veeam Support. Well, Veeam Backup & Replication leverages SMB 3 but that’s an OS feature. Veeam Backup & Replication will work with SMB Multichannel, Direct, Signing, Transparent Failover … It’s out of the Veeam Backup & Replication scope of responsibilities as we have seen here. You feel free to leverage SMB Direct whether that is using iWarp/Roce or Infiniband. This information was confirmed by Veeam and bears the “Anton Gostev seal of approval”. So if SMB Direct cause issues you have a configuration problem with that feature, it’s not Veeam not being able to support it, it doesn’t know or care actually.


The elegance and simplicity of the Veeam Backup & Replication GUI are deceiving. Veeam is extremely powerful and is surprisingly flexible in how you can leverage and configure it. I hope both my previous blog post and this one have given you some food for thought and ideas. There’s more Veeam goodness to come in the coming months when times allows. Many years ago, when SMB 3 was introduced I demonstrated the high availability capabilities this offered for Veeam backups. I’ll be writing about that in another blog post.

Simplified SMB Multichannel and Multi-NIC Cluster Networks

Simplified SMB Multichannel and Multi-NIC Cluster Networks

One of the seemingly small feature enhancements in Windows Server 2016 Failover clustering is simplified SMB multichannel and multi-NIC cluster networks. In Windows 2016 failover clustering now recognizes and uses multiple NICs on the same subnet for cluster networking (Cluster & client access).


Why was this introduced?

The growth in the capabilities of the hardware ( Compute, memory, storage & networking) meant that failover clustering had to leverage this capability more easily and for more use cases than before. Talking about SMB, that now also is used for not “only” CSV and live migration but also for Storage Spaces Direct and Storage Replica.

  • It gives us better utilization of the network capabilities and throughput with Storage Spaces Direct, CSV, SQL, Storage Replica etc.
  • Failover clustering now works with multichannel as any other workload without the extra requirement of needing multiple subnets. This is more important that it seems to me at first. But in many environment getting another VLAN and/or extra subnet is a hurdle. Well that hurdle has gone.
  • For IPv6 Link local Subnets it just works, these are auto configured as cluster only networks.
  • The cluster Validation wizard won’t nag about it anymore and knows it’s a valid failover cluster configuration

See it in action!

You can find a quick demo of simplified SMB multichannel and multi-NIC cluster networks on my Vimeo channel here


In this video I demo 2 features. One is new and that is virtual machine compute resiliency. The other is an improved feature, simplified SMB multichannel and multi NIC cluster networks. The Multichannel demo is the first part of the video. Yes, it’s with RDMA RoCEv2, you know I just have to do SMB Direct when I can!

You can read more about simplified SMB multichannel and multi-NIC cluster networks on TechNet in here. Happy Reading!

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!

Presenting at ITProceed 2015 & E2EVC 2015 Berlin on SMB Direct

You cannot afford to ignore SMB3 and it’s capabilities related to storage traffic such as multichannel, RDMA and encryption. SMB Direct over RoCE seems to have a bright future as it continuous to evolve and improve in Windows Server 2106. The need for DCB (PFC and optionally ETS) intimidates some people. But it should not.

I’ll be putting SMB Direct & RoCE into perspective at ITPROCEED | Welcome to THE IT Pro Event of the year! and #E2EVC E2EVC 2015 Berlin, June 12-14, 2015 Berlin, Germany, sharing experiences, tips and demos!  Come see PFC & ETS in action and learn what it can do for you. Storage vendors should most certainly consider supporting all features of SMB 3 natively as a competitive advantage. So Join me for the talk “SMB Direct – The Secret Decoder Ring”.

All these talks are at extremely affordable community driven events to make sure you can attend. The sessions are given by speakers who do this for the community (speakers and attendees do this in their own time and pay for their our own travel/expenses) and who work with these technology in real life and provide feedback to vendors on the issues or opportunities we see. This makes the sessions very interesting and anything but marketing, slide ware or sales pitches. See you there!