Running a RAID 0 setup and was wondering if running defrag too much would lead to a disk failure faster? Disks fail based on doing too many reads and writes? or is it based on the spinup and spindowns?
Google's study on disk failures is to my knowledge the largest available research from real-life data concerning disk failures. They found a surprisingly small correlation between utilization/temperature/power cycle counts and disk failure. That is, there are other variables that have a larger influence.
Google found that when some specific SMART values started to increase, the drive had a 40 times greater risk of failing within two months as compared to a "healthy" drive, but when working on such a minimal set as one does in a home environment, this is not really anything one can draw any real conclusions from. The sample size is simply too small to draw raw conclusions on almost all parameters for home PC:s concerning disk failure (well, don't let them endure physical stress (drop them, etc.)).
"Is it based on", you say. Well, perhaps to some extent, but probably so small that it is not noticeable in such a small sample.