I came across a really helpfull page of how to troubleshoot vsan performance and all the steps you might need to understand whats happening in your environment and most importantly how to mitigate performance issues.
https://core.vmware.com/resource/troubleshooting-vsan-performance#_Toc536646851
Also very helpfull tools are IO Insight which was added to vSphere 7 Update 1 and IO Trip Analyzer which was added to vSphere 7 Update 3, here some video’s from Duncan Epping about these features:
The original article was posted on: www.hollebollevsan.nl
