RAID? Was: PATA hard disks, anyone?

[Fred Cisin]

Well outside my realm of expertise (as if I had a realm!), . . .

How many drives would you need, to be able to set up a RAID, or hot 
swappable RAUD (Redundant Array of Unreliable Drives), that could give 
decent reliability with such drives?

How many to be able to not have data loss if a second one dies before the 
first casualty is replaced?
How many to be able to avoid data loss if a third one dies before the 
first two are replaced?

How many technicians with shopping carts full of spare drives?
(cf. early vaccum tube computers?)