Explain why a drive is considered "failed"

My Drobo 5C failed a drive that I thing is still good (two and a half years old, less than 500 power-on hours, good S.M.A.R.T attributes, passed internal self-test).

Unfortunately there is no chance to find out why the Drobo considered the drive as failed. So I tried to re-insert the drive, in case the canact was just bad, but that didn’t help.

So I’m requesting some better explanations (i.e. reasoning) for “failed” drive events.

Me too! I’m running a Seagate 8T in my main system that was marked “failed” by the Drobo last year. It passes any diagnostics I can throw at it. It’s also a problem when you try to return a drive under waranty when it passes all their diagnostics. When I first set up my Drobo (5N) it marked two new drives as bad within days of installing them. Recently I had a total system failure that started when I was copying a bunch of files to my main system to organize them, and the Drobo marked a drive as bad during that copy. I replaced it, and during the rebuild it marked ALL drives as bad. Six drives failed in as many days, I find highly suspicious.