Still not sure what I think of HyperFlex I would “Just buy a standard UCS” and install ESX with VSAN, but UCSguru has a good post on sizing HyperFlex.
“Calculating the usable capacity of your HyperFlex cluster under all scenarios is worth taking some time to fully understand
The most significant design decision to take, is whether to optimise your HyperFlex cluster for Capacity or Availability, as with most things in life there is a trade-off to be made.
If you size your cluster for maximum capacity obviously you will lose some availability, likewise if you optimise your cluster for availability you will not have as much usable capacity available to you.
The setting that determines this is the Replication Factor”