storage durability calculators
using similar math from Backblaze durability calculator https://github.com/Backblaze/erasure-coding-durability
google sheets model (not perfect) here https://docs.google.com/spreadsheets/d/140zC6gw6PB6mbxcqyrT5LrXwcg_N5YNhWZ1s5hL-RUg/edit?usp=sharing