The number of redundant drives actually doesn’t make much difference, but it does “help”. Instead of picturing individual drive failures, picture a house fire.

Also picture the next step after one of the drives fails – you’ll be copying all of that data off of your 1 good drive, putting a lot of stress on it. That drive is likely from the same batch, same age, etc. as the failed drive. The likelihood of your good drive failing during the recovery process is higher than one might like.