Matt, I agree.

However, apparently the "broken" HDD is in fact working. I did not manage to get the SMART data from it, as I've only had the time to test if from a USB dock that does not seem to expose those (tried with various HDD test tools), but I could see the drive, make it GPT, create volume, format it, save an read files from it.

Please, notice this is the first time this happened. Of the previous failed drives, two I did check and they had actually failed, others I did not check and simply relied on Drobo telling me they were bad, and then this one.

No obvious pattern to me...