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VDI “The Missing Questions” #8: How does memory density affect VDI scalability?

Can you see it? The end is nigh! The end of this blog series, not necessarily “the end” as in AMC’s the Walking Dead sort of end. Are you Zombie stumbling across this blog from a random Google search? Here is a table of contents to help you on your journey as we once again delve into the depths and address another question on our quest to answer… The VDI questions you didn’t ask, but really should have.

You are Invited!  If you’ve been enjoying our blog series, please join us for a free webinar discussing the VDI Missing Questions, with Tony, Doron, Shawn and Jason!  Access the webinar here!

Got RAM? VDI is an interesting beast both from a physical perspective as well as the care and feeding of it. One thing this beast certainly does like is RAM (and braaaiiiins). Just in case I am still being stalked by that tech writer, RAM stands for Random Access Memory. I spoke a bit about Operating Systems in our 5th question in this series, and this somewhat builds upon that in regards to the amount of memory you should use. Microsoft says Windows 7 needs:
1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit). For the purpose of our testing, we went smack in the middle with 1.5GB of RAM. Does it really matter what we used for this testing? It does a little – one, we need to have sufficient resources for the desktop to perform the functions of the workload test, and second, we need to pre-establish some boundaries to measure from.

Calculating overhead. In order to properly account for memory usage, we need to take into account the overhead of certain things in the Hypervisor.  If you want to learn more about calculating overhead, click here.  Here are a couple of things we are figuring in overhead for:

  1. ESXi = 200MB
  2. VM = 29MB for each 1.5GB, 1vCPU Virtual Desktop

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VDI “The Missing Questions” #7: How memory bus speed affects scale

March 13, 2013 at 11:59 am PST

This was the test I most eagerly anticipated because of the lack of information on the web regarding running a Xeon-based system at a reduced memory speed. Here I am at Cisco, the company that produces one of the only blades in the industry capable of supporting both the top bin E5-2690 processor and 24 DIMMs (HP and Dell can’t say the same), yet I didn’t know the performance impact for using all 24 DIMM slots. Sure, technically I could tell you that the E5-26xx memory bus runs at 1600MHz at two DIMMs per channel (16 DIMMs) and a slower speed at three DIMMs per channel (24 DIMMs), but how does a change in MHz on a memory bus affect the entire system? Keep reading to find out.

Speaking of memory, don’t forget that this blog is just one in a series of blogs covering VDI:

The situation. As you can see in the 2-socket block diagram below, the E5-2600 family of processors has four memory channels and supports three DIMMs per channel. For a 2-socket blade, that’s 24 DIMMs. That’s a lot of DIMMs. If you populate either 8 or 16 DIMMs (1 or 2 DIMMs per channel), the memory bus runs at the full 1600MHz (when using the appropriately rated DIMMs). But when you add a third DIMM to each channel (for 24 DIMMs), the bus slows down. When we performed this testing, going from 16 to 24 DIMMs slowed the entire memory bus to 1066MHz, so that’s what you’ll see in the results. Cisco has since qualified running the memory bus at 1333MHz in UCSM maintenance releases 2.0(5a) and 2.1(1b), so running updated UCSM firmware should yield even better results than we saw in our testing.

 

As we’ve done in all of our tests, we looked at two different blades with two very different processors. Let’s start with the results for the E5-2665 processor. The following graph summarizes the results from four different test runs. Let’s focus on the blue lines. We tested 1vCPU virtual desktops with the memory bus running at 1600MHz (the solid blue line) and 1066MHz (the dotted blue line). The test at 1600MHz achieved greater density, but only 4% greater density. That is effectively negligible considering that the load is random in these tests. LoginVSI is designed to randomize the load.

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EdChat with Cisco Experts on Technology Trends and Solutions

March 11, 2013 at 7:41 am PST

Edu-Virtual-Forum 540x420 Cisco Now v3Education leaders and innovators around the world are transforming education today. Please join us on March 19th (Americas and EMEA) or March 20 (Asia Pacific), for the Cisco Virtual Forum for Education Leaders, to see how they are shaping the future of education.

During this free global conference, which you can attend from the convenience of your desktop or mobile device, you can participate in live roundtable discussions on leading-edge strategies and practical solutions that are improving the quality of education.  The Forum opens with a keynote session with Dr. Larry Johnson, CEO of the New Media Consortium, and Dr. Ellen Junn, Provost and Vice President for Academic Affairs at San Jose State University, on Trends Shaping the Future of Education. The keynote will followed by  breakout sessions for K-12 schools and higher education. There will also be a virtual exhibit hall featuring resources and information on how Cisco solutions can help transform teaching and learning.

The Virtual Forum will also feature live Moderated Chat sessions with Cisco education experts on the technologies supporting the latest trends in education including BYOD, flipped learning, social collaboration, ICT education, desktop virtualization and more. We’ll also include a session in Brazilian Portuguese.

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VDI “The Missing Questions” #5: How does 1vCPU scale compared to 2vCPU’s?

More and more this novel idea of user classifications and workload profiles is being used to separate VDI user allocations. I’ve worked with many customers who prefer to stack rank their users based on the importance of their role/job function and the typical applications that user needs in their role as a means to (hopefully) gain a more appropriate VDI resource allocation. Again – this is a great idea and a good excuse for organizations to take a long hard look at their users and the applications they use day to day.

In case you are finding this blog for the first time, we have been attempting to defy blog physics and host a series of blogs – this requires the use of a manually updated table of contents:

  1. VDI “The Missing Questions” #6: What do you really gain from a 2vCPU virtual desktop? 
  2. VDI “The Missing Questions” #7:  How memory bus speed affects scale
  3. VDI “The Missing Questions” #8: How does memory density affect VDI scalability?
  4. VDI “The Missing Questions” #9: How many storage IOPs?

You are Invited!  If you’ve been enjoying our blog series, please join us for a free webinar discussing the VDI Missing Questions, with Tony, Doron, Shawn and Jason!  Access the webinar here!

Most of the time the three main items separating user classes are:

  1. vCPU quantity
  2. Memory allocation
  3. Disk space

The first sort of pitfall that I see occasionally is too much granularity in the workload profiles. Don’t get me wrong, if you have a good view into your users and applications that you see the need to support and manage 5 different user classifications – that’s great news! But most of the time it comes down to 3 particular types of user classifications:

  1. Gold (Multiple vCPU’s, a lot more RAM and disk space than other folks)
  2. Silver (Could be a couple of vCPU’s, usually more RAM than the OS calls for, can be required for specialized apps, etc)
  3. Bronze (These are almost always single vCPU and minimum amount of RAM profiles)

A good sort of buildup approach to start determining your workload profile requirements must take into consideration the users and compute requirements based on the apps those users will be running. In most cases, the Operating System you choose will be the foundation to start your buildup approach. The aging Windows XP platform is quickly being consumed by Windows 7 in the corporate workspace. There are few folks out there continuing to stand up net new systems for users and using Windows XP. This is for a number of reasons – most new PC’s and their manufacturers (not to mention this little company called Microsoft) are not developing drivers and supporting the workhorse XP operating system. Let’s be honest, Windows XP came out in 2001. Windows XP is older than my twin girls that are in 4th grade! It was a good ride, but it must come to an end. You probably noticed that I haven’t mentioned Windows 8 yet. After all, it is the newest desktop Operating System (OS) that Microsoft has out. There are a couple of reasons for this: Most corporate users don’t jump onto the latest OS because they have to support many users, must test/qualify their applications on a new operating system and as we all know – anything new usually has fixes and enhancements to follow. Plus, as a general rule of thumb, the first Service Pack must come out before anyone will give real consideration to mass deployment in any organization. Beyond the general newness of the Windows 8 OS, it will be interesting to see how “Corporate America” will integrate the new look and feel of Windows 8. With that being said, we have Windows 7 which came out in 2009 and already has Service Pack 1 with a host of subsequent updates. This is the OS that most folks are planning their VDI environments for. Per Microsoft, the requirements for Windows 7 are as follows:

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Distributed VDI for Enterprise Branches

IT managers are in an interesting situation – all the developments in virtualization, compute, and mobility are bringing new opportunities for architecting an efficient IT infrastructure. They are looking for ways to do more with less infrastructure. These developments are accelerating resource centralization, with more and more critical assets moving into the enterprise headquarters and data center and this is creating a ripple effect on branch and remote offices. To meet regulatory compliance and cost-control requirements, many organizations are optimizing resources and reducing complexity in the branch office. Read More »

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