Good actuarials can pull this off. They just charge enough that they can invest some of your upfront payment and use the interest to pay the staff to support you. We know how often hard drives fail, so you just ensure that you have enough interest to replace them when that happens.

If you are the only one paying upfront this is impossible as your harddrives might fail early, but if there are 1000 people willing to pay upfront we can easially handle that.

Note that I would not be surprised if this was just a Ponzi. That we know how to do this doesn't mean we are.