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by Duncan Epping

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vSAN Stretched Cluster vs Fault Domains in a “campus” setting?

Duncan Epping · Sep 25, 2025 · 2 Comments

I got this question internally recently: Should we create a vSAN Stretched Cluster configuration or create a vSAN Fault Domains configuration when we have multiple datacenters within close proximity on our campus? In this case, we are talking about less than 1ms latency RTT between buildings, maybe a few hundred meters at most. I think it is a very valid question, and I guess it kind of depends on what you are looking to get out of the infrastructure. I wrote down the pros and cons, and wanted to share those with the rest of the world as well, as it may be useful for some of you out there. If anyone has additional pros and cons, feel free to share those in the comments!

vSAN Stretched Clusters:

  • Pro: You can replicate across fault domains AND protect additionally within a fault domain with R1/R5/R6 if required.
  • Pro: You can decide whether VMs should be stretched across Fault Domains or not, or just protected within a fault domain/site
  • Pro: Requires less than 5MS RTT latency, which is easily achievable in this scenario
  • Con/pro: you probably also need to think about DRS/HA groups (VM-to-Host)
  • Con: From an operational perspective, it also introduces a witness host, and sites, which may complicate things, and at the various least requires a bit more thinking
  • Con: Witness needs to be hosted somewhere
  • Con: Limited to 3 Fault Domains (2x data + 1x witness)
  • Con: Limited to 20+20+1 configuration

vSAN Fault Domains:

  • Pro: No real considerations around VM-to-host rules usually, although you can still use it to ensure certain VMs are spread across buildings
  • Pro: No Witness Appliance to manage, update or upgrade. No overhead of running a witness somewhere
  • Pro: No design considerations around “dedicated” witness sites and “data site”, each site has the same function
  • Pro: Can also be used with more than 3 Fault Domains or Datacenters, so could even be 6 Fault Domains, for instance
  • Pro: Theoretically can go up to 64 hosts
  • Con: No ability to protect additionally within a fault domain
  • Con: No ability to specify that you don’t want to replicate VMs across Fault Domains
  • Con/Pro: Requires sub-1ms RTT latency at all times, which is low, but will be achievable in a campus cluster, usually

#103 – The performance impact of Memory Tiering featuring Qasim Ali and Todd Muirhead

Duncan Epping · Sep 22, 2025 · Leave a Comment

The last few months, I’ve had many discussions about Memory Tiering. When I saw a brand new performance white paper being released, I knew it was time to invite two of the authors to the podcast. Qasim Ali and Todd Muirhead go over the ins and outs of Memory Tiering, they discuss the basics, but also explain in-depth what the potential performance impact is when enabling this feature in your environment. You can listen on Apple Podcasts, Spotify, the embedded player below, or any podcast app of your choice!

If you’d like to know more, visit the following links!

  • ⁠Performance blog⁠
  • ⁠Performance white paper⁠
  • ⁠Explore Session Arvind and David⁠
  • ⁠Explore Session Dave⁠
  • ⁠Extreme Performance Series videos⁠
  • ⁠How to enable Memory Tiering blog⁠
  • ⁠VMware Performance Blog

#102 – Explore on Tour featuring Joe Baguley and friends!

Duncan Epping · Sep 8, 2025 · Leave a Comment

We just finished Explore in Las Vegas, and the various local ⁠Explore On Tour events⁠ are literally around the corner. I will most likely be in London, Frankfurt, and potentially Paris myself. It looks like Joe Baguley will also be at all of those events delivering the keynote! Why should you go? Well, listen to the episode to find out. We start out with a brief conversation with Joe, and then have Frank Denneman, Martin Hosken, and Lars Fiechtner joining to provide their insights! My call to action, if you are planning on attending, register as soon as registration is open as London sold out fast, and so did the UK VMUG the day after! Listen to the episode on Spotify (bit.ly/3VEnWLw), Apple (bit.ly/4pawc3l), or via the embedded player below or your podcast app of choice!

#101 – Discussing VCF 9.0 and Private AI Foundation with NVIDIA enhancements with Frank Denneman!

Duncan Epping · Aug 4, 2025 · Leave a Comment

It was time to get Frank Denneman back on the show to discuss the enhancements introduced in VCF 9 and Private AI Foundation with NVIDIA. Frank goes over all new functionality and all the enhancements like Agent Builder etc. Frank also mentioned various must-attend sessions at Explore, register now, as these will fill up fast:

  • ⁠Chris Wolf, keynote and breakout⁠
  • ⁠Shawn Kelly and Justin Murray: Accelerating AI Workloads⁠
  • ⁠Frank’s AI/ML sessions⁠!

You can listen to the episode on Apple Podcasts, Spotify, or anywhere else you find your podcasts! Of course, you can also simply use the embedded player below.

#100 – What is the Google Cloud VMware Engine all about? Featuring Sai Gopalan and Ken Bocchino

Duncan Epping · Jul 21, 2025 · Leave a Comment

Episode 100, YESSSS! Finally, we managed to get there. For this episode, I invited two Google Cloud VMware Engine (GCVE) product managers to explain what GCVE is all about. We had Dr. Wade Holmes on the show, 84 episodes ago, to introduce GCVE, so it was time to re-introduce GCVE and discuss the current solution, and the benefits it brings with for instance the flexibility in node types, bring your own licensing, disaster recovery, networking, and much more. Ken and Sai had some interesting stories, so make sure to pay close attention! Listen via the embedded player below, or simply go to your favorite podcast player and find the episode there! (Spotify, Apple)

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About the Author

Duncan Epping is a Chief Technologist and Distinguished Engineering Architect at Broadcom. Besides writing on Yellow-Bricks, Duncan is the co-author of the vSAN Deep Dive and the vSphere Clustering Deep Dive book series. Duncan is also the host of the Unexplored Territory Podcast.

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