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VDI – The Questions You Didn’t Ask (But Really Should)

There’s no shortage of content out there (a quick Google search easily confirms this) when it comes to looking for vendor-originated material touting the latest server performance benchmarks for hosted virtual desktops.  Being part of that community, I’m pretty sure I have my fingerprints on more than one such piece of collateral – and I’m constantly reminded of this, when we run into questions along the lines of “yeah, {xxx} desktops on a blade is great, but c’mon, you and I both know we’d never do that in practice”.  It’s a balancing act of demonstrating solution performance, intersected with the practical reality of what IT managers would reasonably support in a production environment.

So what really matters?  If I’m implementing VDI for the 1st time, and I’m trying to make intelligent decisions around CPU, memory speed, IOPS, etc., where do I go?  VDI is unique in its consumption of compute, storage and network resources, when compared to other workloads hosted in the data center.  Much of the performance benchmarking info put out by server manufacturers is not specific to VDI performance, or how user experience might be impacted by simple decisions like choice of clock speed or # of vCPU.

Thankfully, there are folks in my company that care a LOT about such questions.  So much so, that a small, VDI-proficient group of them took it upon themselves to design and build an in-house lab environment with one express purpose – exhaustively exploring and documenting the performance and scalability impacts seen when configuring your compute platform for VDI.  No stone left unturned – things like CPU cores, clock speed, memory speed,  vCPU, memory density and more – all fair game.

The findings are extremely valuable to anyone deploying VDI, and what this team discovered is a set of real-life “questions”.  The “Missing” questions if you will – those questions that are noticeably absent or never sufficiently exposed in marketing materials, when it comes to the practical choices you can make that most significantly impact the cost, scalability and performance of your virtual desktop implementation.

So let me start with an introduction.  Over the next few weeks, you’re going to hear from some peers of mine – Doron Chosnek, Jason Marchesano, and Shawn Kaiser.  They’re Cisco Consulting Systems Engineers, and they live and breathe VDI (I know, melodramatic), as implemented in their customers’ data centers around the world.

They undertook this journey with the express purpose of answering the “missing” questions, by assembling a test platform in their lab, built on Cisco Unified Computing System (UCS), using readily available components including:

  • Various UCS B200 M3 configurations
  • Login Virtual Session Indexer (Login VSI) 3.6.1 benchmark
  • Login VSI’s Medium with Flash workload
  • VMware View 5.1.1
  • Microsoft Windows 7 SP1 32-bit virtual desktops
  • Pure Storage FlashArray with Purity version 2.0.2.

Keep in mind that their goal was not to explore maximum scalability, or prescribe a preferred design/architecture, or even what kind of server blade or processor you should use for VDI.  Instead they relied on commonly available gear easily found in our customer’s data centers.  If you want prescriptive design guidance, Cisco CVD’s are ideal for that, and you can find them here.

So let’s talk about their test environment.

Physical Lab

The physical environment shown below is a highly overprovisioned system.  Only one B200 M3 blade was tested at any one time, yet every logical link between elements shown consists of multiple 10-GbE links or multiple 8-Gb Fibre Channel links.

The storage array has 24 flash disks and is capable of substantially higher IOPS than used for this testing. All the infrastructure machines used for this test (Active Directory, VMware vCenter, VMware View, VSI Launchers) are virtual machines on the B230 M2 blade in the environment.

9 Q Figure 1

 

Note: At the time of testing, the Pure Storage had not completed UCS certification testing.

 

Logical Server Environment

9 Q Figure 2

The tests involved two UCS B200 M3 blades, one with dual E5-2665 processors and the other with dual E5-2643 processors.  The 2643 is a 4-core high clock/burst speed processor, and the 2665 is an 8-core medium/high clock/burst speed processor.  Here are the specs for the CPU’s chosen:

9 Q Figure 3

Now, you may wonder, are either of these THE processor you would choose for VDI?  Not necessarily! 

Keep in mind the goal we set out with – to expose the relative impacts of # cores, clock speed, memory speed, #vCPU’s etc.  What you’ll take away from the results, are guidance on which parameters matter for specific types of VDI deployments.  You can then safely look at a VDI-“workhorse” processor like the E5-2680 or E5-2690, and apply what our CSE’s have learned through this testing, to that class of CPU, and make your best selection there.

The tests were conducted using Login VSI’s Medium with Flash workload generator.  As we explore the test results in this series, you’ll see reference to “VSImax”, which defines the threshold past which the user experience will be unacceptable.  The VSImax threshold will appear on supporting graphs that show the performance curve under various test scenarios.  You can learn more about how this threshold is derived here.

9 Q Table 1

So that’s the test environment.  Through this series – let’s call it VDI – the Questions You Didn’t Ask (But Really Should) – our CSE friends (Shawn, Doron, and Jason) will explore and expose the findings they’ve documented for us, dealing with a new “question” each time.  If you join us for this journey, it’ll be worth your while – you’ll come away with a better appreciation of the impact that some simple decisions in your data center compute configuration can make.

So are you ready for the journey - You'll find the Questions (answered thus far) below:

  1. VDI “The Missing Questions” #1: Core Count vs. Core Speed
  2. VDI “The Missing Questions” #2: Core Speed Scaling (Burst)
  3. VDI “The Missing Questions” #3: Realistic Virtual Desktop limits
  4. VDI “The Missing Questions” #4: How much SPECint is enough
  5. VDI “The Missing Questions” #5: How does 1vCPU scale compared to 2vCPU’s?
  6. VDI “The Missing Questions” #6: What do you really gain from a 2vCPU virtual desktop?
  7. VDI “The Missing Questions” #7: How memory bus speed affects scale
  8. VDI “The Missing Questions” #8: How does memory density affect VDI scalability?
  9. VDI “The Missing Questions” #9: How many storage IOPs?
  10. VDI "The Missing Questions" Conclusion

Special Web Event - You're Invited!

If you're enjoying our series, be sure to join our free webcast, where Shawn, Doron and Jason will discuss all the (Missing) VDI Questions Live + take your Q&A.  Access the webcast here.

Featured Whitepaper Now Available!

Need a convenient whitepaper-ized version of the discussion?  Download it now, here.

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1 Comments.


  1. January 27, 2013 at 10:45 am

    Interesting, can't wait for more info.

       0 likes