Category Archives: Networking

Know What Receive Side Scaling (RSS) Is For Better Decisions With Windows 8

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Introduction

As I mentioned in an introduction post Thinking About Windows 8 Server & Hyper-V 3.0 Network Performance there will be a lot of options and design decisions to be made in the networking area, especially with Hyper-V 3.0. When we’ll be discussing DVMQ (see DMVQ In Windows 8 Hyper-V), SR-IOV in Windows 8 (or VMQ/VMDq in Windows 2008 R2) and other network features with their benefits, drawbacks and requirements it helps to know what Receive Side Scaling (RSS) is. Chances are you know it better than the other mentioned optimizations. After all it’s been around longer than VMQ or SR-IOV and it’s beneficial to other workloads than virtualization. So even if you’re a “hardware only for my servers” die hard kind of person you can already be familiar with it. Perhaps you even "dislike” it because when the Scalable Networking Pack came out for Windows  2003 it wasn’t such a trouble free & happy experience. This was due to incompatibilities with a lot of the NIC drivers and it wasn’t fixed very fast. This means the internet is loaded with posts on how to disable RSS & the offload settings on which it depends. This was done to get stability or performance back for application servers like Exchange and others applications or services.

The Case for RSS

But since Windows 2008 these days are over. RSS is a great technology that gets you a lot better usage of out of your network bandwidth and your server. Not using RSS means that you’ll buy extra servers to handle the same workload. That wastes both energy and money. So how does RSS achieve this? Well without RSS all the interrupt from a NIC go to the same CPU/Core in multicore processors (Core 0).  In Task Manager that looks not unlike the picture below:

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Now for a while the increase in CPU power kept the negative effects at bay for a lot of us in the 1Gbps era. But now, with 10Gbps becoming more common every day, that’s no longer the case. That core will become the bottle neck as that poor logical CPU will be running at 100%, processing as much network interrupts in can handle, while the other logical CPU only have to deal with the other workloads. You might never see more than 3.5Gbps of bandwidth being used if you don’t use RSS. The CPU core just can’t keep up. When you use RSS the processing of those interrupts is distributed across al cores.

With Windows 2008 and Windows 2008 R2 and Windows 8 RSS is enabled by default in the operating system. Your NIC needs to support it and in that case you’ll be able to disable or enable it. Often you’ll get some advanced features (illustrated below) with the better NICs on the market. You’ll be able to set the base processor, the number of processors to use, the number of queues etc. That way you can divide the cores up amongst multiple NICs and/or tie NICs to specific cores.

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So you can get fancy if needed and tweak the settings if needed for multi NIC systems. You can experiment with the best setting for your needs, follow the vendors defaults (Intel for example has different workload profiles for their NICs) or read up on what particular applications require for best performance.

Information On How To Make It Work

For more information on tweaking RSS you take a look at the following document http://msdn.microsoft.com/en-us/windows/hardware/gg463392. It holds a lot more information than just RSS in various scenarios so it’s a useful document for more than just this.

Another good guide is the "Networking Deployment Guide: Deploying High-Speed Networking Features". Those docs are about Windows 2008 R2 but they do have good information on RSS.

If you notice that RSS is correctly configured but it doesn’t seem to work for you it’ might be time to check up on the other adaptor offloads like TCP Checksum Offload, Large Send Offload etc. These also get turned of a lot when trouble shooting performance or reliability issues but RSS depends on them to work. If turned off, this could be the reason RSS is not working for you..

Thinking About Windows 8 Server & Hyper-V 3.0 Network Performance

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Introduction

The main purpose of this post is, as mentioned in the title, to think. This is not a design or a technical reference. When it comes to designing a virtualization solution for your private cloud their are a lot of components to consider. Storage, networking, CPU, memory all come in to play and there is no one size fits all. It all depends on your needs, budget in combination with how good your  insight into your future plans & requirements are. This is not and easy task. Virtualizing 40 webservers is very different from virtualizing SQL Server, Exchange or SharePoint.  Server virtualization is different from VDI and VDI itself comes in many different flavors.

  • So what workloads are you hosting? Is it a homogeneous or a heterogeneous environment?
  • What kind of applications are you supporting? Client-Server, SOA/Web Services, Cloud apps?
  • What storage performance & features do you need to support all that?
  • What kind of network traffic does this require?
  • What does your business demand? Do you know, do they even know? Can you even know in a private cloud environment?
  • Do you have one customers or many (multi tenancy) and how are they alike or different in both IT needs and business requirements.

The needs of true public cloud builders are different from those running their own private clouds in their own data centers or in a mix of those with infrastructure at a hosting provider. On top of that an SMB environment is different from large enterprises and companies of the same size will differ in their requirements enormously due to the nature of their business.

I’ve written about virtualization and CPU considerations before (NUMA, Power Save settings for both OS & 10Gbps network performance) before. I’ve also discussed a number of posts about 10Gbps networking and different approaches on how to introduce it with out breaking the bank. In 2012 I intend to blog some more on networking and storage options with Windows 8 and Hyper-V 3.0. But I still need to get my hands on the betas and release candidates of Windows 8 to do so. You’ll notice I don’t talk about Infiniband. Well I just don’t circulate in the ecosystems where absolute top notch performance is so important that they can justify and get that kind of budget to throw at those needs.

To set the scene for these blog posts I’ll introduce some considerations around networking options with Hyper-V. There are many features and options both in hardware, technologies, protocols, file systems. Even when everything is intended to make live simpler people might get lost in all the options and choices available.

Windows Server 8 NIC features – The Alphabet Soup

  • Data Center Bridging (DCB)
  • Receive Segment Coalescing (RSC)
  • Receive Side Scaling (RSS)
  • Remote Direct Memory Access (RDMA)
  • Single Root I/O Virtualization (SR-IOV)
  • Virtual Machine Queue (VMQ)
  • IPsec offload (IPsecTO)

A lot of this stuff has to do with converged networks. These offer a lot of flexibility and the potential for cost savings along the way. But convergence & cost savings are not a goal. They are means to an end. Perhaps you can have better, cheaper and more effective solutions leveraging you existing network infrastructure by adding some 10Gbps switches & NICs where they provide the best bang for the buck. Chances are you don’t need to throw it all out and do a fork lift replacement. Use what you need from the options and features. Be smart about it. Remember my post on A Fool With A Tool Is Still A Fool, don’t be that guy!

Now let’s focus on couple of the features here that have to do with network I/O performance and not as much convergence or QOS. As an example of this I like to use Live migration of virtual machines with 10Gbps. Right now with one 10Gbps NIC I can use 75% of the bandwidth of a dedicated NIC for live migration. When running 20 or more virtual machines per host with 4Gbps to 8Gbps of memory and with Windows 8 giving me multiple concurrent Live Migrations I can really use that bandwidth. Why would I want to cut it up to 2 or 3Gbps in that case. Remember the goal. All the features and concepts are just tools, means to and end. Think about what you need.

But wait, in Windows 8 we have some new tricks up our sleeve. Let’s team two 10Gbps NICs put all traffic over that team and than divide the bandwidth up and use QOS to assure Live Migration gets 10Gbps when needed but without taking it away from others network I/O when it’s not needed. That’s nice! Sounds rather cool doesn’t it and I certainly see a use for it. It might not be right if you can’t afford to loose that bandwidth when Live Migration kicks in but if you can … more power & cost savings to you. But there are other reasons not to put everything on one NIC or team.

RSS, VMQ, SR-IOV

One thing all these have in common is that they are used to reduce the CPU load / bottleneck on the host and allow to optimize the network I/O and bandwidth usage of your expensive 10Gbps NICs. Both avoiding having a CPU bottleneck and optimizing the use of the available bandwidth mean you get more out of your servers. That translates in avoiding buying more of them to get the same workload done.

RSS is targeted at the host network traffic. VMQ and SR-IOV are targeted at the virtual machine network traffic but in the end the both result in the same benefits as stated above. RSS & VMQ integrate well with other advanced windows features. VMQ for examples can be used with the extensible Hyper-V switch while RSS can be combined with QOS & DCB in storage & cluster host networking scenarios. So these give you a lot of options and flexibility. SR-IOV or RDMA is more focused on raw performance and doesn’t integrate so well with the more advanced features for flexibility & scalability. I’ll talk some more on this in future blog posts.

Now with all these features that have there own requirements and compatibilities you might want to reconsider putting all traffic over one pair of teamed NICs. You can’t optimize them all in such a scenario and that might hurt you. Perhaps you’ll be fine, perhaps you won’t.

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So what to use where and when depends on how many NICs you’ll use in your servers and for what purpose. For example even in a private cloud for lightweight virtual machines running web services you might want to separate the host management & cluster traffic from the virtual machine network traffic. You see RSS & VMQ are mutually exclusive. That way you can use RSS for the host/cluster traffic and DVMQ for the virtual machine network. Now if you need redundancy you might see that you’ll already use 2*2NIC with Windows 8 NLB in combination with two switches to avoid a single point of failure. Do your really need that bandwidth for the guest servers? Perhaps not but, you might find that it helps improve density because of better better host & NIC performance helping you avoiding the cost of buying extra servers. If you virtualize SQL servers you’d be even more interested in all this. The picture below is just an illustration, just to get you to think, it’s not a design.

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I’m sure a lot of matrices will be produced showing what features are compatible under what conditions, perhaps even with some decision charts to help you decide what to use where and when.

DELL PowerConnect 8024F Is Now Stackable

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A colleague pointed me the latest firmware update (4.2.0.4) for the DELL PowerConnect 8024F switches. As I was reading the release notes one item in particular caught my attention. The PowerConnect 8024/8024f/M8024-k switches are now stackable. You can put up to 6 switches in one stack using the regular front ports (SFP+). You might remember form a previous blog post on 10Gbps, Introducing 10Gbps With A Dedicated CSV & Live Migration Network (Part 2/4), where I mentioned that we got a great deal on those switches. I also mentioned that the only thing lacking in these switches and what would make this the best 10Gbps switch when comparing value for money is the ability to stack them. I quote myself:

“They could make that 8024F an unbeatable price/quality deal if they would make them stackable.”

I’ve been called visionary before but I won’t go into that that insider joke right now Winking smile. Now it’s for sure that not just my little blog post that made this update happen but it is a nice New Year’s gift. More features & options with hardware you already own is always nice. So I guess a lot of people have made the same observation, both customers & DELL themselves. You could just “smell” by the available command & configuration that this switch could be made stackable and they did.

Is Ethernet based stacking perfect? No (there is very little perfection in this world). The biggest drawback, if you need that feature,  is the fact that you can hot plug the stacking links. But for all other practical purposes it’s a nice deal. Why? Well, now that these switches supports Ethernet based stacking you will be able to choose more types of NIC Teaming to use for your servers. That means those teaming configurations that are dependent on stacking, such as for active-active NIC Teaming across two switches to be more precise. I find this pretty good news.

You all know I’m very enthusiastic to use the NIC Teaming build into Windows 8 and I will use it where and when I can. But there will be for many years to come a lot of Windows 2008 R2 systems to support and install. So it’s always good to see your hardware vendors improving their gear to give you more options. For the pricing I got on the 8024F in the last project and the needs of the solution we could deal with not being able to stack. Stacking via Ethernet using other switches was way more expensive, not even to mention the ones using stacking module ones (real premium pricing). So we got the best deal for our needs.

For 10Gbps switches stacking over Ethernet give you up to 80Gbps with a maximum of 8 uplinks so bandwidth is not as much a concern. With 1Gbps switches it is, which makes stacking modules the only way to go there I think. If you need massive bandwidth and you probably do. The drawback, as with all forms of inter switch links (a LAG for example) is that this method means you’re losing ports for other purposes. But you need to look at your needs and do the math. I think buying with investment protection is good but don’t always buy in preparation for the time you’ll become a fortune 500 company. That takes a while and in the mean while you’ll be very well served anyway.

Another related feature that’s new is Nonstop Forwarding (NSF). NSF allows the forwarding plane of stack units to continue forwarding packets even while the control and management planes restart. This could be a power failure, some hardware of software error or even an upgrade. This feature is common to all stackable switches as far as I know and is needed. Not that ‘m saying the redundant loop in stack is bad or overkill, far from it, but that takes care of other scenarios that NSF is designed to handle.

Full Steam Ahead With Windows 8 & Hyper-V in 2012

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Some History

There have been a good number of people who’ve always used, some a lot more and some others a lot less, a bit of Microsoft bashing to gain some extra credibility or try to position other products as superior. Sometimes this addressed, at least, some real challenges and issues with Microsoft products. A lot of the time it doesn’t. I have always found this ridiculous. In the early years of this century I was told to get out of the Microsoft stack and into the LAMP stack to make sure I still had a job in a few years’ time. My reaction was to buy Inside SQL Server 2000 among other technology books Smile. The paradox is that in some cases, like some storage integrators, is that the ones doing the bashing are forgetting that their customers are often heavily invested in the Microsoft stack.

I Still Have A Job

As you might have realized already, I still have a job today. I’m very busy, building more and better environments based on Microsoft technologies. Microsoft does not get everything right. Who does? Sometimes it takes more than a few tries, sometimes they fail. But they also succeed in a lot of their endeavors.They are capable to learn, adapt and provide outstanding results with a very good support system to boot (I would dare say that you get out of that what you put into it). Given the size and nature of the company, combined with IT evolving at the speed of light, that’s not an easy task.

Today that ability translates into the upcoming release of Windows 8. Things like Hyper-V 3.0, the new storage and networking features, the improvements to clustering and the file system are the current state an evolution. A path along Windows 2000 over Windows 2003(R2), to  the milestone Windows 2008 which was improved with Windows 2008 R2. Now, Windows 8 being the next generation improves vastly on that very good and solid foundation. With Windows 8 we’ll take the next step forward in building highly scalable, highly available, feature rich a very functional solutions in a very cost effective manner. On top of that we can do more now than ever before, with less complexity and with affordable  standard hardware. If you have a bigger budget, great, Windows 8 will deliver even more and better bang for the buck if and when your hardware vendors get on the band wagon.

Windows 8 & Storage

One of the things the Windows BUILD Conference achieved is that it wanted me to buy hardware that I couldn’t get yet. Just try asking DELL or HP for RDMA support on 10Gbps and you get a bit of a vacant blank stare.

Another thing is that it made me look at our storage roadmap again. One of the few sectors in IT that are still very expensive is storage. Some of the storage vendors might start to feel a bit like a major network gear vendor. You know the one that has also seen the effects of serious competition by high quality but lower cost kit. Just think about what Storage Pools/Spaces will do for affordable, easy to use and rich storage solutions. Both with standard over the shelf available (read affordable) hardware and with modern SANs that leverage the Windows 8 features there is value. Heath my warning storage vendors. You’re struggling in the SMB market due to complexity, cost and way to much overhead and expensive services. Well it’s only going to get worse. You’ll have to come with better proposals or you’ll end up being high end / niche market players in the future. Let’s face it, if I can buy a super micro chassis with the disks of my choosing I can build my own storage solution for cheap and use Windows 8 to achieve my storage needs. Perhaps is 80/20 but hey, that’s great. It’s not that much better with more expensive solutions (vendor disks are ridiculously over priced) and the support process is sometimes a drain on your workforce’s time and motivation. And yes you paid for that. Compare this with being able to buy some spare parts on the cheap and having it all available of the shelf with the vendors. No more calls, no more bureaucratic mess for return parts, nor more IT illiterate operators to work through before you reach support that can be sub standard as well. Once you reach a certain level of hardware quality there is not that much difference any more except for price and service. Granted, some vendors are better at this then others. The really big ones often struggle getting this right.

I’ve been in this business long enough to know that all stuff breaks. SLAs are fine for lawyers and for management. CYA is part of doing business. But for the IT Pro in the field you need reliable people, gear and services.  On top of that you have to design for failure. You know things will break. So it should be a cheap, easy and fast as possible to fix while your design and architecture should cope with the effects of a failure. That’s what IT Pros need and that what’s keeps things running (not that SLA paper in the mailbox of your manager).

Show the Windows customers a bit more love than you have done in the past. Some in the storage industry tend to like to look down on the Windows OS. But guess what, it is your largest customer base. Unless you want to end up in the same niche as a very expensive personal trainer for Hollywood stars (tip: there’s not a huge job market there) you’d better adjust to new realities. A lot of them are doing that already , some of them aren’t. To those: get over it and leverage the features in Windows 8. You’ll be able to sell to a more varied public and at the high end you’ll have even better solutions to offer. Today I notice way to many storage integrators who haven’t even looked at Windows 8. It’s about time they started … really, like today. I mean how do you want to sell me storage today if you can’t answer my queries on Windows 8 & System Center 2012 support and integration? To me this is huge! I want to know about ODX, RDMA, SMI-S and yes I want you to be able to answer me how your storage deals with CSVs. You should know about the consumption of persistent ISCSI-3 reservations and a rock solid hardware VSS provider. If you can do that it creates the warm fuzzy feeling a customers need to make that leap of faith.

When I look at the network improvements in Windows 8. Things like RDMA, SMB 2.2; File Transfer Offload and what that means for file sharing and data intensive environments I’m pretty impressed. Then there is Hyper-V 3.0 and it many improvements. Only a fool would deny that it is a very good, affordable & rich hypervisor with a bright future as far as hypervisors go (they are not the goal, just a means to an end). Live Storage Migration, an extensible virtual switch, monitoring of the virtual switch, Network Virtualization, Hyper-V Replica, … it’s just too much to mention here. But hop on over to Windows 8 Hyper-V Feature Glossary by Aidan Finn. He’s got a nice list up of the new features relevant to the Hyper-V crowd. Again, we see improvements for all business sizes, from SMB to enterprise, including the ISPs and Cloud providers. Windows 8 is breaking down barriers that would interdict it’s use in various environments and scenarios. Objections based on missing features, scalability, performance or security in multi tenancy environments are being wiped of the map. If you want to see some musing on this subject just look at Group Video Interview: What is your favorite Hyper-V feature in Windows 8?.

2012 & Beyond

Hyper-V is growing. It’s already won a lot of hearts and minds of many smaller Microsoft shops but it’s also growing in the enterprise. The hybrid world is here when you look at the numbers, even if it’s not yet the case in your neck of the woods. Why? Cost versus features. Good enough is good enough. Especially when that good is rather great. On top of that the integration is top notch and it won’t cost you a fortune and save you a lot of plumbing hassle.

Basically everyone can benefit from all this. You’ll get more and better at a lesser or at least a more affordable cost. Even if you don’t use any Microsoft technologies you’ll benefit from the increased competition. So everyone can be happy.