when the snow field is 2T do i have to a use 2T ssd? it is possible use several smaller ssd together for 2t snowfield? what will the minimum disk size for each smaller ssd? and is that economical ?

You can combine

Easy way would be software raid

But arktika miner can also do it

wild promises of 5GB/s reads are starting to appear https://www.anandtech.com/print/14449/phisons-ps5016e16-ps5019e19-the-worlds-first-pcie-40-ssd-controllers Phison’s PS5016-E16 & PS5019-E19: The First PCIe 4.0 Client SSD Controllers