You will naturally like to see what equipment you need and what enhancements you can make with these needs before you invest for a new vSan Environment
There are several manufacturer tools that I share links with below that you can perform automatically.
Click here for vSan Readynode Sizer and here for Vxrail Xpress Sizer.
So what should you do if you want to do an average calculation without having to depend on these tools?
vSAN Stretched Cluster (SC) provides business continuity in multiple failure situations like Fault Domains. Data is written simultaneously to two separate locations, the first location is called Preferred and the second one is called Secondary. If one of the locations is lost, the virtual machines restarts at the second location by using VMware HA, where all fresh data exists.
In this article I will explain the subject of vSAN Fault Domains. You can review the original source here.
Fault Domains allow systems to run in cases where multiple server failures or a cabinet is not reachable by spreading the vSAN cluster across multiple cabinets or blade chassis. One or more servers can be added to each Fault Domain.