I've seen this several times as I am in the data recovery business. And yes they often do fail at the same time, however I don't believe this has anything to do with when they were built necessarily, as I've also seen it happen with mismatched drives. Most often this type of failure occurs shortly after a thunder storm, power surge, or power outage. Typically the surge damages the drives or RAID controller, and within a few days they start failing. I'm actually working right now on recovering an array that had two drives fail simultaneously after a power outage. (looks hopeless right now)

TIP: Surge protectors don't really protect your equipment. Always connect your raid 5 to a good UPS. I've never seen this happen when the array was on a UPS.

I've seen this several times as I am in the data recovery business. And yes they often do fail at the same time, however I don't believe this has anything to do with when they were built necessarily, as I've also seen it happen with mismatched drives. Most often this type of failure occurs shortly after a thunder storm, power surge, or power outage.

Typically the surge damages the drives or RAID controller, and within a few days they start failing. I'm actually working right now on recovering an array that had two drives fail simultaneously after a power outage. (looks hopeless right now)

A little tip: Surge protectors don't really protect your equipment. Always connect your raid 5 to a good UPS. I've never seen this happen when the array was on an UPS.