The expected dose for their treatment was 50 rads, and they received 300-400. http://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/ucm185898.htm. Trying to downplay their dose by comparing it to the therac-25 is a little bit like comparing virtue among whores. They were burned by their dose.

Now be nice. He is right, 0.07% is correct.

The chance of any one failing is the same as 1 - the chance of none failing. If you have n gadgets with a risk of failure of m, the risk of any one or more failing is 1-((1-m)^n). For 0.01% (0.0001) and 7, that puts your risk of any disk failing at about 0.07%. 1 - (1 - 0.0001 ) ^ 7) = 0.0006997901 ... or about 0.07%.

The idea is the chance of any one or more failing is really the flip side of the chance of none failing. If any item has a p chance of happening, then the chance of them all happening is p1 * p2 * ... pn. So, if we have a chance of one drives survival at .9999, the likelyhood that all will survive is that 0.9999 ** 7.