Jsk1957
Contributor
Contributor

VSAN Cluster topolgy support

Hello,

In the Network guide it mentions that you can have a VSAN cluster non stretched among (3) sites. We have (2) FX2's Blade chassis that we would like to put each one at two different sites that are near to each other. As long as we meet the network requirements, will this work without configuring it as a stretch cluster? Or do we need to use Fault Domains which would require another FX2?

Thanks,

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5 Replies
TheBobkin
VMware Employee
VMware Employee

Hello Jsk1957

Yes, you can connect physically separate vSAN nodes in a non-stretched cluster provided they have low enough latency between the nodes (<1ms) - however this may not be ideal and not recommended for All-Flash unless your network is extremely low latency between the 'sites'.

Bob

rphoon
Contributor
Contributor

Technically it would work but you are exposing yourself to greater risks such as split-brain scenario when your link between your data center fails.

Furthermore, to use fault domains, the minimum number is 3 if PFTT=1 as mentioned in Managing Fault Domains in vSAN Clusters.

If you have 2 FX2 chassis, I would recommend creating a stretched cluster with each FX2 chassis per site as the witness will act as a tie-breaker during link-loss scenarios.

If you do not have a 3rd site to put the witness, it can be placed in the public cloud as well as mentioned in the following article.

The vSAN Witness Appliance in vCloud Air: Part 1 (Overview) - Virtual Blocks

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RAJ_RAJ
Expert
Expert

Hi ,

Could you please share how many blade servers will be available on each Fx2 chassis .

I hope you planning to create a vSan Cluster   with esxi nodes inside two chassis  and both are reachable through network .

RAJESH RADHAKRISHNAN VCA -DCV/WM/Cloud,VCP 5 - DCV/DT/CLOUD, ,VCP6-DCV, EMCISA,EMCSA,MCTS,MCPS,BCFA https://ae.linkedin.com/in/rajesh-radhakrishnan-76269335 Mark my post as "helpful" or "correct" if I've helped resolve or answered your query!
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Jsk1957
Contributor
Contributor

There only (2) FC630 blades in each FX2. With a stretch cluster we wouldn't be able to configure SFTT for each site.

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memmaker
Contributor
Contributor

Please see vSAN network guide.

https://storagehub.vmware.com/export_to_pdf/vmware-r-vsan-tm-network-design

**While most vSAN deployments are within the same room in the same data center, VMware supports having vSAN nodes in different rooms and different sites without stretched cluster and without a dedicated witness. However, this is only supported when the latency is at LAN levels, which is <1ms. In these configurations, one would need to use also Fault Domains to implement availability across room or across site. Please refer to the appropriate vSAN documentation for steps on how to do this.

so your configration, if I am correct.

you have total 4 hosts. right? (2 blades per each chassis)

each host is fault domain, so you would have 4 fault domains. unless you don't configure rack awareness.

with 4 FD, you will not have problem.

if you have only 2 hosts. 2 node vsan deployment you can consider. however it required witness host in third place.

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