The Data-Dragon has undergone 14 drive tests, and most have tested all 13 of the 4 TB disks. A total of 648 TB (648,127,498,862,592 bytes actually) of data was written and verified as a result. Despite some setbacks caused by controllers, I have fairly high confidence these drives are functional.
So what caused the problems with the original Data-Dragon setup? Unknown. For now we will have to live with this answer. The Data-Dragon is setup with ZFS in RAIDz2, meaning it can survive a two drive failure. There is also a backup server whose drives are normally spun down. Thus there should be little chance of such a failure occurring again.
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