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Introducing 10Gbps & Thoughts On Network High Availability For Hyper-V (Part 3/4)

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This is a 3th post in a series of 4. Here’s a list of all parts:

  1. Introducing 10Gbps Networking In Your Hyper-V Failover Cluster Environment (Part 1/4)
  2. Introducing 10Gbps With A Dedicated CSV & Live Migration Network (Part 2/4)
  3. Introducing 10Gbps & Thoughts On Network High Availability For Hyper-V (Part 3/4)
  4. Introducing 10Gbps & Integrating It Into Your Network Infrastructure (Part 4/4)

As you saw in my previous blog post “Introducing 10Gbps With A Dedicated CSV & Live Migration Network (Part 2/4)” we created an isolated network for Hyper-V cluster networking needs, i.e. Heartbeat, Cluster Shared Volume and Live Migration traffic. When you set up failover clustering you’re doing so to achieve some level of high availability. We did this by using 2 switches and setting up redundant paths to them, making use of the fault tolerance the cluster networks offer us. The darks side of high availability is that is always exposes the next single point of failure and when it comes to networking that means you’ll need redundant NICs, NIC ports, cabling and switches. That’s what we’ll discuss in this blog post. All the options below are just that. There is never an obligation to use them everywhere and it might be not needed depending on the type of network and the business needs we’re talking about. But one thing I have learned is to build options into your solutions. You want ways and opportunities to work around issues while you fix them.

Redundant Switches

The first thing you’ll need to address is the loss of a switch. The better ones have redundant power supplies but that’s about it. So you’ll need to have (at least) two switches and make sure you have redundant connections to both switches. That implies both switches can talk to each other as they form one functional unit even when it is an isolated network as in our example.

One of the ways we can achieve this is by setting up a Link Aggregation Group (LAG) over Inter Switch Links (ISL). The LAG makes all the connections available between the switches for the VLANs you define. There are different types of LAG but one of the better ones is a LAG with LACP.

Stacking your switches might also be a solution if they support that. You might need stacking modules for that. Basically this turns two or more switches into one big switch. One switch in the stack acts as the master switch that maintains the entire stack and provides a single configuration and monitoring point. If a switch in the stack fails the remaining switches will bypass the failed switch via the stacking modules. Depending on the quality of your network equipment you can have some disruption during a the failure of the master switch as then another switch needs to take on that role and this can take anything between 3 seconds and a minute depending on vendor, type, firmware, etc. Network people like this. And as each switch contains the entire the stack configuration it’s very easy to replace a dead switch in a stack. Just rip out the dead one, plug in the replacement one and the stack will do the rest.

We note that more people have access to switches that can handle LAGs versus those who have stackable ones. The reason for this is that the latter tend to be more pricy.

Redundant Network Cards & Ports

Now whether you’re using LAGs or stacking the idea is that you connect your NICs to different switches for redundancy. The question is do we need to do something with the NIC configuration or not to benefit from this? Do we have redundancy in via a cluster wide virtual switch or not? If not can we use NIC teaming? Is NIC teaming always needed or a good idea? Ok, let’s address some of these questions.

First of all, Hyper-V in the current Windows Server 2008 SP1 version has no cluster wide virtual switch that can provide redundancy for your virtual machine network(s). But please allow me to dream about Hyper-V 3.0. To achieve redundancy for the virtual machine networks you’ll need to turn to NIC teaming. NIC teaming has various possible configurations depending on vendor and the capabilities of the switches in use. You might be familiar with terminology like Switch Fault Tolerance (SFT), Adaptive Fault Tolerance (AFT), Link Aggregation Control protocol (LACP), VM etc. Apart from all that the biggest thing to remember is that NIC teaming support has to come from the hardware vendor(s). Microsoft doesn’t support it directly for Hyper-V and Hyper-V gets assess to a NIC team NIC via the Windows operating system.

On NIC Teaming

I’m going to make a controversial statement. NIC teaming can be and is often a cause of issues and it can expensive in time to both set up and fix if it fails. Apart from a lot of misconceptions and terminology confusion with all the possible configurations we have another issue. NIC teaming introduces complexity with drivers & software that is at least a hundred fold more likely to cause failures than today’s high quality network cards. On top of that sometimes people forget about the proper switch configuration. Ouch!

Do a search on Hyper-V and NIC teaming and you’ll see the headaches it causes so many people. Do you need to stay away from it? Is it evil? No, I’m not saying that. Far from that, NIC teaming is great. You need to decide carefully where and when to use it and in what form. Remember when you can handle & manage the complexity need to achieve high availability, generally speaking you’re good to go. If complexity becomes a risk in itself, you’re on the wrong track.

Where do I stand on NIC teaming? Use it when it really provides the benefits you seek. Make sure you have the proper NICs, Switches and software/drivers for what you’re planning to do. Do your research and test. I’ve done NIC Teaming that went so smooth I never would have realized the headaches it can give people. I’ve done NIC teaming where buggy software and drivers drove me crazy.

I’d like to mention security here. Some people tend to do a lot of funky, tedious configurations with VLANS in an attempt to enhance security. VLANS are not security mechanisms. They can be used in a secure implementation but by themselves they achieve nothing. If you’re doing this via NIC teaming/VLANS I’d like to note that once someone has access to your Hyper-V management console and /or the switches you’re toast. Logical and physical security cannot be replaced or ignored.

NIC Teaming To Enhance Throughput

You can use NIC teaming enhance bandwidth/throughput. If this is you major or only goal, you might not even be worried about using multiple switches. Now NIC teaming does help to provide better bandwidth but, sure but nothing beats buying 10Gbps switches & NICs. Really, switches with LAGs or stack and NIC Teaming are great but bigger pipes are always better for raw throughput. If you need twice or quadruple the ports only for extra bandwidth this gets expensive very fast. And if, on top of that, you need consultants because you don’t have a network engineer to set it all up just for that purpose, save your money and invest it in hardware.

NIC Teaming For Redundancy

Do you use NIC teaming for redundancy? Yes, this is a very good reason when it fits the needs. Do you do this for all networks? No, it depends. Just for heartbeat, CSV & Live migration traffic it might be overkill. The nature of these networks in a Hyper-V Cluster is such that you don’t really need it as they can mutually provide redundancy for each other. But what if a NIC port fails when I’m doing a live migration? Won’t that mean the live migration will fail? Yes. But once the NIC is out of the picture Live Migration will just work over the CSV network if you set it up that way. And you’re back in business while you fix the issue. Have I seen live migration fail? Yes, sure. But it never left the VM messed up, that kept running. So you fix the issue and Live Migrate it again.

The same goes for the other networks. CSV should not give you worries. That traffic gets queued and send to the next available network available for CSV. Heart beat is also not an issue. You can afford the little “down time” until it is sent over the next available network for cluster communication. Really a properly set up cluster doesn’t go down when a cluster networks fails if you have multiple of them.

But NIC teaming could/would prevent even this ever so slight interruption you say. It can, yes, depending on how you set this up, so not always by definition. But it’s not needed. You’re preventing something benign at great cost. Have you tested it? Is it always a lossless, complete transparent failover? No a single packet dropped? Not one ping failed? If so, well done! At what cost and for what profit did you do it? How often do your NICs and switch ports fail? Not very often. Also remember the extra complexity and the risk of (human) configuration errors. As always, trust but verify, testing is your friend.

Paranoia Is Your Friend

If you set up NIC teaming without separate NIC cards (not ports) and the PCIe slot goes bad NIC teaming won’t save you. So you need multiple network cards. On top of that, if you decide to run all networks over that team you put all your eggs in that one basket. So perhaps you might need 2 teams distributed over multiple NIC cards. Oh boy redundancy and high availability do make for expensive setups.

Combine NIC Teaming & VLANS Work Around Limited NIC Ports

This can be a good idea. As you’ll be pushing multiple networks (VLANs) over the same pipe you want redundancy. So NIC teaming here can definitely help out. You’ll need to consider the amount of network traffic in this case as well. If you use load balancing NIC teaming you can get some extra bandwidth, but don’t expect miracles. Think about the potential for bottle necks, QoS and try to separate bandwidth hogs on separate teams. And remember, bigger pipes are always better, so consider 10Gbps when you are in a bandwidth crunch.

Don’t Forget About The Switches

As a friendly reminder about what we already mentioned above, don’t forget to use different switches for up linking the NIC ports. If you do forget your switch is the single point of failure (SPOF). Welcome to high availability: always hitting the net SPOF and figuring out how big the risk is versus the cost in money and complexity to deal with it J. Switches don’t often fail but I’ve seen sys admins pull out the wrong PDU cables. Yes human error lures in all corners in all possible variations. I know this would never happen to you, and certainly not twice, but other people are not so skillful. And for those who’d rather be lucky than good I have bad news. Luck runs out. Inevitably bad things happen to all of our systems.

Some Closings Thoughts

One rule of thumb I have is not to use NIC teaming to save money by reducing NIC Cards, NIC ports, number of switches or switch ports. Use it when it serves your needs and procure adequate hardware to achieve your goals. You should do it because you have a real need to provide the absolute best availability and then you put down the money to achieve it. If you talk the talk, you need to walk the walk. And while not the subject of this post, your Active Directory or other core infrastructure services are not single points of failure , are they? Winking smile

If you do want to use it to save money or work around a lack of NIC ports, there is nothing wrong with that, but say so and accept the risk. It’s a valid decision when you have you have your needs covered and are happy with what that solution provides.

When you take all of this option into consideration, where do you end with NIC teaming and network solutions for Hyper-V clusters? You end up with the “Business ready” or “reference architecture” offered by DELL or HP. They weigh all pros and cons against each other and make a choice based on providing the best possible solution for the largest number of customers at acceptable costs. Is this the best for you? That could very well be. It all depends. They make pretty good configurations.

I tend to use NIC teaming only for the Virtual Machine networks. That’s where the biggest potential service interruption exists. I have in certain environments when NIC teaming was something that was not chosen mediated that risk by providing 2 or 3 single NIC for 2 or 3 virtual networks in Hyper-V. That reduced the impact to 1/3 of the virtual machines. And a fix for a broken NIC is easy; just attach the VMs to a different virtual network. You can do this while the virtual machines are running so no shutdown is required. As an added benefit you balance the network traffic over multiple NICs.

10Gbps with NIC teaming and VLANs provide for some very nice scenarios. This is especially true especially if you have bandwidth hungry applications running in boatload of VMs. This all means that we need to start thinking and talking about integrating the 10Gbps switches in our network infrastructure. So that means we’re entering the network engineers their turf and we’ll need to address some of their concerns. But this is not bad news as they’ll help us prevent some bad scenarios. But that will be discussed in a next blog post.

10Gbps Bragging Right Nothing More

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Well, when you get to play with some 10Gbps network gear, experiment a little you see some pretty nice file copy transfer times. But things are not very consistent. “It all depends”. So do experiment a lot & test things out. At a given moment you get rewarded with this:

That’s right. The most successful experiment was 61% of a 10Gbps pipe used and the file transfer speed for a 25GB vhd file was in one word amazing. We used jumbo frames and we disabled (same old story) except for the fact that this kind of throughput turns the receiving server in shell shocked piece of hardware. During the 35 seconds, it could get anything else done, bar for those poor disks. Perhaps you’ll want to throttle it down a little in a production environment.

Introducing 10Gbps With A Dedicated CSV & Live Migration Network (Part 2/4)

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This is a 2nd post in a series of 4. Here’s a list of all parts:

  1. Introducing 10Gbps Networking In Your Hyper-V Failover Cluster Environment (Part 1/4)
  2. Introducing 10Gbps With A Dedicated CSV & Live Migration Network (Part 2/4)
  3. Introducing 10Gbps & Thoughts On Network High Availability For Hyper-V (Part 3/4)
  4. Introducing 10Gbps & Integrating It Into Your Network Infrastructure (Part 4/4)

Introduction

In this post we continue along the train of thought we set in a previous blog post “Introducing 10Gbps Networking In Your Hyper-V Failover Cluster Environment (Part 1/4)”. Let’s say you want to set up a Hyper-V cluster for SQL Server virtualization. Your business & IT manager told you the need to provide them with the best performance you can get. They follow up on that statement with a real budget so you can buy high end servers (blades or rack) and spec them out optimally for SQL Server. You take into consideration NUMA issues, vCPU:pCPU ratios, SQL memory demands, the current 4 vCPU limit in hyper-V, etc. By the way, this will be > 16vCPU with Windows Server 8, which leads me to believe the 64GB memory ceiling for virtual machines will also be broken. But for now this means that with regard to CPU & memory you’ve done all you can. That leaves only networking and IO to deal with. Now the IO is food for another & very extensive discussion, but basically you have to design that around the needs of the application(s) or you’ll be toast. The network part is what we’ll tackle here.

Without going into details, what does a Hyper-V cluster need in terms of networking?

Who/What Function Traffic Connection Type
Host Management Hyper-V host connectivity. Relatively low bandwidth. But don’t forget about deploying VMs or backups. Public
VM Network Provides network connectivity to the VMs Very dependent on the VMs using it. Dedicated Hyper-V
Cluster Heartbeat Internal cluster communication to determine the status of other cluster nodes Not much traffic but low latency or cluster might think it’s in trouble due to dropped packets. OK to combine with CSV. Private Cluster Network
Cluster Shared Volume (CSV) For updating CSM metadata & scenarios where redirected I/O is required Mostly idle. When in redirected I/O it demands high bandwidth & low latency required. Private Cluster Network
Live Migration Used to transfer the running VM’s from one cluster node to another Mostly idle. When Live Migrating it demands high bandwidth & low latency required. Private Cluster Network

Host Management: It is fine to leave this on 1Gbps, unless you have a need to deploy massive amounts of VMs or you backups are consuming all bandwidth. If so consider dedicated NICs for those roles and/or 10Gbps. Also note that you might be able to leverage your SAN for virtual machine deployment / backups.

VM Network: Use multiple “single” NICs or NIC teams to spread both the load and the risk. Remember that you can lose the host management or CSV network of a node, without affecting your virtual machine connectivity but not the virtual machine network(s). So don’t put all your eggs in one basket. So do consider multiple NICs and NIC teaming. Do remember that there are other bottle necks than bandwidth to a virtual machine running apps so don’t go completely overboard as there is no single magic bullet here for virtual machine performance. 2 or 3 will do perfectly fine. What about backups in the guest? Yes, that’s an extra burden but there are better solutions than that and if you hit and bandwidth issue with guest based backups it’s time to investigate them seriously. As you will see in these series I’m not a mincer with NIC ports but there’s no need to have one for every 2 Virtual machines. If you have really high bandwidth needs consider 10Gbps, not a truck load of NIC ports.

Heartbeat: Due to the mostly moderate needs it is often combined with the CSV traffic.

Cluster Shared Volume (CSV): Well you have the need for metadata of the clustered shared volumes. But that’s not all. You also have redirected access when you’re doing backups, defragmenting your CSV storage or when the storage paths are unavailable. So go for 10Gbps when you can, especially since this is your backup path for Live Migration traffic!

Side Note: Don’t say that Redirected Access over the CSV network will never happen when you have redundant storage paths. We’ve seen it happen in an environment with dual FC HBA cards, dual SAN controllers and the works. Redirected Access saved our service availability during that event! What happened exactly and how it all ties together is a long story and complicated but in essence an arbitrated loop management module when haywire and caused a loop, the root cause of this was a defective disk. When that event was over one of the controllers went nuts and decided this wasn’t his cup of tea and called it a day. Guess what? Some servers could not failover to the other controller as something went wrong in the internal workings of the SAN itself, dual HBA didn’t help here. How did our services stay available? Thanks to Redirected Access. It was at 1Gbps speeds so that hurt a little but we kept ‘m running. Our vendor worked through this with us but things where pretty bad and it was pucker time. However this is one example where we kept our services running for 24 hours (whilst working at the issue with the vendor) via redirected access. The bad thing was we needed to take the spare controller of line & restart both to get the replacement controller to be recognized, yes a complete shutdown of the cluster nodes to restart both SAN controllers. I still remember the mail I send and the call I made to management that is was shutting down the business for 30 minutes. But it was not because of Hyper-V, quite the opposite; it helped us out a lot!

Also note that when you run software VSS based backups and disk defragmentation on your CSV storage you’ll be running in Redirected Access mode. Also see https://blog.workinghardinit.work/2011/06/02/some-feedback-on-how-to-defrag-a-hyper-v-r2-cluster-shared-volume/ Some Feedback On How to defrag a Hyper-V R2 Cluster Shared Volume

Live Migration: The bigger and better the pipe the faster Live Migration gets done. With high density or resource (memory) intensive servers this becomes a lot more important. Think of SQL Server, Exchange consuming 16, 24, 32 or more GB of memory. So do consider 10Gbps.

iSCSI: As we are using Fiber Channel in our SAN we did not include iSCSI in the networking needs table above. Now I do want to draw your attention to the need for iSCSI in the virtual machines themselves. This is needed for clustering within the virtual machines. Today this is almost a requirement as clustering in the guest becomes more and more important. You’ll need at least two NIC ports in production for this, if possible in on two separate cards for ultimate redundancy. Now as a best practice we won’t share the iSCSI NICS between the hosts and the guests. I do this in the lab but won’t have it in production. So that could mean at least two more NIC ports. With 10Gbps you’ll have ample performance but depending on your IO needs you might want 4 if you’re using 1Gbps so those NIC numbers are rising fast.

What Function Traffic Connection Type
iSCSI Guest Virtual machine shared storage. High bandwidth need, low latency is required to get good I/O Dedicated to Hyper-V
iSCSI host Host shared storage High bandwidth need, low latency is required to get good I/O Excluded from cluster, dedicated to the host.

What to move to 10Gbps?

Cool, you think, let’s throw some 10Gbps NICs & switches into our network. After that, depending on the rest of your network equipment & components, your virtual machines might be able to talk to other virtual and physical servers on the network at speeds up to 10Gbps or at least 1Gbps. I kind of hope that none of you are running 100 Mbps in your server racks today. And last but not least, with your 10Gbps network you’ll be able to do get the best performance for your CSV and Live Migration traffic. Life is good!

Until your network engineer hears about your plans. All of a sudden it’s no so cool anymore. You certainly woke the network people up! They’re nervous now they have seen all the double (redundancy) lines you’ve drawn on your copy of the schema representing the rack / server room network. They start mumbling things about redundancy, loops, RSTP, MSTP, LAG, stacking and a boatload other acronyms that sound like you’ve heard ‘m before but can’t quite place. They also talk about doom and gloom scenarios that might very well bring down the network. So unless you are the network admin you should dust of your communication skills and get them on board. So for your sake I hope they’re not the kind of engineers that states that most network problems that can’t be solved by removing servers and applications that ruin the nirvana of their network design. If so they’ll be vary weary of that “virtual switch” you’re talking about as well.

The Easy Way Out – A Dedicated CSV & Live Migration Network

Let’s say that you need a lot more time to get to a fully integrated solution for the 10Gbps network architecture figured out and set up. But your manager states you need to improve the Live Migration and other cluster network speeds today. What are your options? Based on the above information your boss is right, the networks that will benefit the most from a move to 10Gbps are CSV and Live Migration (and Heart Beat that piggy backs along with CSV). Now you have to remember that those cluster networks (subnets/VLANs) are for the Heart Beat, CSV and Live Migration cluster traffic only. So basically the only requirement you have is that these run on separate subnets/VLANs (to present them as distinct networks to your failover cluster) and that every node of the cluster can communicate over those subnets/VLANs. This means that you can leave the switches for those networks completely isolated from the rest of the network as shown in the picture below. I used some very common and often used DELL PowerConnect switches (5424, 6248, 8024F) in some scenario drawings for this blog series. They could make that 8024F an unbeatable price/quality deal if they would make them stackable. The sweet thing about stackable switches is that you can do Active-Active NIC teaming across switches rather than active-passive. I never went that way as I’m waiting to see what virtual switch innovations Hyper-V 3.0 will bring us. You see I’m a little cheap after all

But naturally, feel free to think about these scenarios with your preferred ProCurves, CISCO, Juniper, NetGear … switches in mind.

Suddenly things are cool again. The network people get time to figure out an integrated & complete long term solution and you can provide your nodes with 10Gbps for cluster only traffic. By a couple of 10Gbps switches & NICs and you’re on your way. Is this a good idea? I can’t make that call for you. I just provide some ideas. You decide.

The Case For Physically Isolating Them

Now you might wonder if this isn’t very wasteful in resources. Well not necessarily. If your cluster is big enough, let’s say 12-16 nodes or if you have a couple of clusters (4 clusters with 5 nodes for example) this might be not overly expensive. Unless you’re on a converged network, you do (I hope) the same for your storage networks, isolate them that is. You have to when you’re using fiber and you’d better do it when using iSCSI. It provides for the best performance and less complex switch configurations. Remember I mentioned that high availability requires some complexity. Try to keep that complexity as low as possible and when you introduce complexity make sure you can manage it. This serves two purposes. One is making sure that the complexity doesn’t ruin your high availability and two is that you’ll be happy you did it when it comes to troubleshooting and fixing issues. Now you might say that this ruins the concept of converged networks. Academically this is true but when you are filling up ports on switches for a single purpose there is no room for anything else anyway. Don’t lose sight of the aim of a converged network. That is to have the ability to use the same hardware/technology when possible for multiple needs. This gives you options and capabilities where and when needed. It’s not about always using all technology and protocols on each and every switch. Don’t forget also that you’ll need to address QOS/Performance on a converged network per type of traffic. There is also the fact that in brownfield scenario’s you’re dealing with replacing a part of the infrastructure and this example is a good way to get 10Gbps where needed and not making any change on the existing network infrastructure. This reduces risk and impact. As a matter of fact if you plan this right you can do this without service interruption. That means going node by node (maintenance mode, evacuate all VMs), moving the CSV network first for example, and only then the Live Migration network. You’re leveraging the ability of the cluster networks to take on each other’s role here to achieve this.

Another good reason to physically isolate the networks is security. There was an exploit for manipulating VMs during live migrations in 2008 (http://www.eecs.umich.edu/techreports/cse/2007/CSE-TR-539-07.pdf). You can protect against this via very careful switch configuration and VLAN design. But isolating the switches is very easy, clean, and effective as well. Overkill? I don’t know, but perhaps not if you do work for intelligence agencies.

Ethernet Out-of-Band (OOB) Port For Management

Don’t forget you still need to be able to manage those switches but today, in this class of equipment you get an Ethernet Out-of-Band (OOB) port for that. This one you can safely uplink to your regular management network. So if you really don’t need communication with the rest of the network you have no functional reason not to isolate them.

Money, Cost? No Value!

Still, you think, isn’t this very expensive? Well, look at the purpose. Manageable complexity, high availability, and your management stated to eliminate, where possible, any limitation on performance and approved the budget for it all. Put this into perspective. The SQL Server data center editions running on these clusters, combined with the cost of development & maintenance of the databases and applications relying on this infrastructure put that extra money spent on a couple of switches really into perspective. On top of that, you’re not wasting those switches. When the network people get their plans finished they’ll be integrated into the final solution if still needed and possible. Don’t forget that you might use all ports for just cluster traffic depending on the number of hosts you have! So even without integrating them into the rest of the network, you’re still getting very solid results. On top of that, sometimes you get to build solutions where budget is not the first, last, and only concern. Sweet! I do know some people who’ll call me a money-wasting nut case J. But get real, when you’re building highly available, highly performing failover clusters and you’re in a discussion about the cost of a couple of NIC ports and you are going to adjust your design over that, perhaps you have a sponsorship issue. Put this into perspective. Building a Hyper-V cluster is not a competition where the one who uses the least NIC ports/cards and switch ports/ switches win. That’s why it hurts when I see designs like this claiming victory:

What I want to see is more like this:

But that will never fit into a blade design! Really? Have you seen the blades like the DELL M910? It’s a beast, comparable to the R810. It’s was the first blade I really felt like buying. Cisco also entered that market with guns drawn and is pushing HP to keep performing. So Again put the NIC/Switch and NIC port/Switch Port count into perspective against what you’re trying to achieve. To quote Anton Ego “… you know what I’m craving? A little perspective, that’s it. I’d like some fresh, clear, well-seasoned perspective.”

Introducing 10Gbps Networking In Your Hyper-V Failover Cluster Environment

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This is a 1st post in a series of 4. Here’s a list of all parts:

  1. Introducing 10Gbps Networking In Your Hyper-V Failover Cluster Environment (Part 1/4)
  2. Introducing 10Gbps With A Dedicated CSV & Live Migration Network (Part 2/4)
  3. Introducing 10Gbps & Thoughts On Network High Availability For Hyper-V (Part 3/4)
  4. Introducing 10Gbps & Integrating It Into  Your Network Infrastructure (Part 4/4)

A lot of early and current Hyper-V clusters are built on 1Gbps network architectures. That’s fine and works very well for a large number of environments. Perhaps at this moment in time you’re running solutions using blades with 10Gbps mezzanine cards/switches and all this with or without cutting up the bandwidth available for all the different networks needs a Hyper-V cluster has or should have for optimal performance and availability. This depends on the vendor and the type of blades you’re using. It also matters when you bought the hardware (W2K8 or W2K8R2 era) and if you built the solution yourself or bought a fast track or reference architecture kit, perhaps even including all Microsoft software and complete with installation services.

I’ve been looking into some approaches to introducing a 10Gbps network for use with Hyper-V clusters mainly for Clustered Shared Volume (CSV) and Live Migration (LM) Traffic. In brown field environments that are already running Hyper-V clusters there are several scenarios to achieve this, but I’m not offering the “definite guide” on how to do this. This is not a best practices story. There is no one size fits all. Depending on your capabilities, needs & budget you’ll approach things differently, reflecting what’s best for your environment. There are some “don’t do this in production whatever you environment is” warnings that you should take note of, but apart from that you’re free to choose what suits you best.

The 10Gbps implementations I’m dealing with are driven by one very strong operational requirement: reduce the live migration time for virtual machines with a lot of memory running a under a decent to heavy load. So here it is all about bandwidth and speed. The train of taught we’re trying to follow is that we do not want introduce 10Gbps just to share its bandwidth between 4 or more VLANs as you might see in some high density blade solutions. There that has often to do with limited amount of NIC/switch ports in some environments where they also want to have high availability. In high density scenarios the need to reduce cabling is also more urgent. All this is also often driven a desire to cut costs or keep those down as much as possible. But as technology evolves fast my guess is that within a few years we won’t be discussing the cost of 10Gbps switches anymore and even today there very good deals to be made. The reduction of cabling safes on labor & helps achieve high density in the racks. I do need to stress however that way too often discussions around density, cooling and power consumption in existing data centers or server rooms is not as simple as it appears. I would state that the achieve real and optimal results from an investment in blades you have to have the server room, cooling, power and ups designed around them. I won’t even go into the discussion over when blade servers become a cost effective solutions for SMB needs.

So back to 10Gbps networking. You should realize that Live Migration and Redirected Access with CSV absolutely benefit from getting a 10Gbps pipes just for their needs. For VMs consuming 16 Gb to 32 GB of memory this is significant. Think about it. Bringing 16 seconds back to 4 seconds might not be too big of a deal for a node with 10 to 15 VMs. But when you have a dozen SQL Servers that take 180 to 300 seconds to live migrate and reduce that to 20 to 30 seconds that helps. Perhaps not so during automated maintenance but when it needs to be done fast (i.e. on a node indicating serious hardware issues) those times add up. To achieve such results we gave the Live Migration & CSV network both a dedicated 10Gbps network. They consume about 50% of the available bandwidth so even a failover of the CSV traffic to our Live Migration network or vice versa should be easily handled. On top of the “Big Pipes” you can test jumbo frames, VMQ, …

Now the biggest part of that Live Migration time is in the “Brown-Out” phase (event id 22508 in the Hyper-V-Worker log) during which the memory transfer happens. Those are the times we reduce significantly by moving to 10Gbps. The “Black-Out” phase during which the virtual machine is brought on line on the other node creates a snapshot with the last remaining delta of “dirty memory pages”, followed by quiescing the virtual machine for the last memory copy to be performed and finally by the unquiescing of the virtual machine which is then running on the other node. This is normally measured in hundreds of milliseconds (event id 22509 in the Hyper-V-Worker log) . We do have a couple of very network intensive applications that sometimes have a GUI issue after a live migration (the services are fine but the consoles monitoring those services act up). We plan on moving those VMs to 10Gbps to find out if this reduces the “Black-Out” phase a bit and prevents that GUI of acting up. When can give you more feedback on this, I’ll let you known how that worked out.

An Example of these events in the Hyper-V-Worker event log is listed below:

Event ID 22508:

‘XXXXXXXX-YYYY-ZZZZ-QQQQ-DC12222DE1’ migrated with a Brown-Out time of 64.975 seconds.

Event ID 22509:

‘XXXXXXXX-YYYY-ZZZZ-QQQQ-DC12222DE1’ migrated with a Black-Out time of 0.811 seconds, 842 dirty page and 4841 KB of saved state.

Event ID 22507:

Migration completed successfully for ‘XXXXXXXX-YYYY-ZZZZ-QQQQ-DC12222DE1’ in 66.581 seconds.

In these 10Gbps efforts I’m also about high availability but not when that would mean sacrificing performance due to the fact I need to keep costs down and perhaps use approaches that are only really economical in large environments. The scenarios I’m dealing with are not about large hosting environments or cloud providers. We’re talking about providing the best network performance to some Hyper-V clusters that will be running SQL Server for example, or other high resource applications. These are relatively small environments compared to hosting and cloud providers. The economics and the needs are very different. As a small example of this: saving a ten thousand switch ports means that you’ll need you’ll save 500 times the price of a switch. To them that matters a lot more, not just in volume but also in relation to the other costs. They’re probably running services with an architecture that survives loosing servers and don’t require clustering. It all runs on cheap hardware with high energy efficiency as they don’t care about losing nodes when the service has been designed with that in mind. Economics of scale is what they are all about. They’d go broke building all that on highly redundant hardware and fail at achieving their needs. But most of us don’t work in such an environment.

I would also like to remind you that high availability introduces complexity. And complexity that you can’t manage will sink your high availability faster than a torpedo mid ship downs a cruiser. So know what you do, why and when to do it. One final piece of advice: TEST!

So to conclude this part take note of the fact I’m not discussing the design of a “fast track” setup that I’ll resell for all kinds of environments and I need a very cost effective rinse & repeat solution that has a Small, Medium & Large variety with all bases covered. I’m not saying those aren’t good or valuable, far from it, a lot of people will benefit from those but I’m serving other needs. If you wonder why they want to virtualize the applications at all, it has to do with disaster recovery & business continuity and replicating the environment to a remote site.

I intend to follow up on this in future blog posts when I have more information and some time to write it all up.