@ibsteve2u
First, yes, consumer drives aren't designed for RAID. Back in the IDE days, WD drives were failing left and right in RAID, so they decided to certify their business drives in a "RAID Edition" series. Usually most "Enterprise SATA" drives are capable of RAID but it's best to check with the vendor.
Now here's the big thing about defects:
It isn't rocket science how manufacturers come up with warranties. When they produce a lot of one product (a factory "lot", not "many", although it means pretty much the same thing....semantics) they do QA (quality assurance) testing. This is also something that many consumers don't believe. QA testing is all about finding out how many defects are produced in a given lot. This is where it gets interesting though. You see, mass volume manufacturers can't test every unit out of a lot of, say, 10,000. Instead, they might pull maybe one in every hundred off the assembly line, test it, and continue. Out of that x # of units, so many are going to come back defective. They estimate that the original percentage is representative of the whole, just like how the TV Neilson ratings estimate the numbers of TV watchers based on a much smaller model.
If the defect rate is abnormally high, then that entire lot will often carry a shorter warranty because they expect failures. In the case of products that have multiple distribution channels, some channels have a lesser warranty than others. OEM hard drives, for instance. It used to be that OEM drives only carried a 1 year warranty and retail carried more. Then it was the other way around. Now they're approximately even, although external drives still get the shaft (which is why you shouldn't buy an external drive during these flood prices).
Here's a good example of how warranties are calculated though: look at Seagate's problems over the last few years with firmware. Only a few years ago they touted a 5 year warranty across the board, then when they started having mass failings of drives they reduced it to 3. This year, it's now only 2 years. That's not a coincidence. What's happening is the price to bear the warranty service is costing them too much because of the sheer number of defects.
Here's another fact: computer makers pay far less for their parts than you or I buying retail-boxed components. Why? They buy in bulk, but they also buy parts with higher defect rates. Why you think they only cover systems for 1 year? Don't you think that if they got parts that had the same warranty coverage as the retail channel that the parts would be reliable enough for them to cover the entire system for the same length of warranty that the components had?
So there's a lesson here too: when you build a system yourself with retail components with more than a 1 year warranty, it's actually going to be more reliable, and the warranty is proof of that. When you buy a name brand computer it's not statistically going to be as reliable, and an extended warranty is just insurance to cover failures. It isn't any more reliable just because you pay extra to extend that 1 year warranty.
