Yellow Bricks

by Duncan Epping

design

Limit your Cluster Size to 8?

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Lately I have been seeing more and more people recommending to limit clusters to eight hosts. I guess I might be more or less responsible for this “myth“, unintentionally of course as I would never make a recommendation like that.

My article was based on the maximum amount of VMs per host in a HA cluster with 9 hosts or more. The current limit is 40 VMs per host when there are 9 hosts or more in a cluster. With a maximum of 1280 VMs per cluster. (32 hosts x 40 VMs)

So why this post? I want to stress that you don’t need to limit your cluster based on these “limitations”. Just think about it for a second, how many environments do you know where they have 40+ VMs running on every single host? I don’t know many environments where they do exceed these limits, I guess exceptions are VDI environments…

So why would you want to “risk” exceeding these limits? Simple answer: TCO. Having two clusters is more expensive than a single a cluster. For those who don’t understand what I am trying to say: N+1. In the case of a single cluster you will have 1 spare host. In the case of two clusters you will have two spare hosts in total.

Another justification for a single cluster is DRS. More hosts in a cluster leads to more opportunities for DRS to balance the cluster. A positive “side effect” is also that the chances of resource congestion are reduced because there are more VM placement combinations possible.

Is there a recommendation? What is the VMware Best Practice? There simply isn’t one that dictates the cluster size. Although the maximums should be taken into consideration for support you should calculate your cluster size based on customer requirements and not on a max config sheet.

Document it…

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Something that I noticed over the last months while doing design reviews is that hardly anyone documents decisions in a design. Most designs I review are physical designs, which is understandable as most IT people are technical people who could not care less about logical designs. I am perfectly fine with that, although I do recommend taking a different approach, as long as you document why you are going down a specific path.

There can be specific constraints or requirements (both technical and business related) which justify your decision, but if you don’t document these constraints or requirements chances are someone will change the design based on a false assumption and who knows what it will lead to…

Congrats to those that passed the Design Exam

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Finally, the results have been emailed today. Congrats to all of you who passed the exam! (And those who didn’t, I’m sure you will next time now you know what to expect.) I know at least a couple of you bloggers passed: Heino(Virtual troll) and Rick Scherer(VMware Tips). Of course there are some more names floating around on twitter.

Again congrats and I will see you guys during one of the “defense” sessions, have fun and good luck on your preparations.

VMworld 2009 – TA2259 Ask the Experts Panel Session

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We are proud to officially announce the VMworld 2009 – Ask the Experts Panel Session.  This session will feature virtualization experts Rick Scherer, Scott Lowe, Duncan Epping, Chad Sakac and Tom Howarth answering your questions on virtual infrastructure design.  In the next week or so we will be posting sections on our blog sites for you to submit questions for review during the session, so stay tuned!

Session ID: TA2259
Session Title: Ask the Experts – Virtualization Design
Track: Technology and Architecture
Abstract: Are you running a virtual environment and experiencing some problems?  Are you planning an upgrade from VI3 to vSphere 4 and have some questions about the infrastructure architecture changes required?  Do you have a virtual infrastructure design and want it blessed by the experts?  Come join us for a one hour panel session where your questions are the topic of discussion!  Join the Virtualization Experts; Rick Scherer from VMwareTips.com, Scott Lowe author of Mastering vSphere 4, Duncan Epping from VMware, Chad Sakac from EMC and Tom Howarth from planetVM.net as they answer your questions on virtualization design.

I shamelessly copied this from vmwaretips.com… But I don’t think Rick will mind the extra promotion for this session!

I still owed you guys a picture…

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I still owed you guys something. Here’s the list of the people that where awarded the VCDX certification during the VMware TS vSummit 2009 in San Francisco:

  1. John Arrasjid (US)
  2. Mostafa Khalil (US)
  3. Kamau Wanguhu(US)
  4. Andrew Hald (US)
  5. Mahesh Rajani (US)
  6. Craig Risinger (US)
  7. Duncan Epping (Netherlands)
  8. Richard Damoser (Germany)

The vSummit award dinner was on Wednesday evening. Unfortunately Spencer Critchlow(VCDX 009, UK), Aidan Dalgleish(VCDX 010, UK) and Paul Nothard(VCDX 011, UK) were all scheduled on Friday and that’s why they are not in the picture. On the picture, but not VCDX’s: Melissa Tuite and Enis Konuk.

From left to right:
John Arrasjid, Mostafa Khalil, Craig Risinger, Enis Konuk, Melissa Tuite, Andrew Hald, Kamau Wanguhu, Duncan Epping, Richard Damoser and Mahesh Rajani.

I want to thank Thomas MacKay for the picture!