Apparently disk drives have all kinds of cool things they can do besides reporting your typical “OMG I’m going to fail soon!” messages. Seagate reports that nearly 80% of the “failed” disks they receive are actually fine. They cannot find any issues whatsoever. What does Seagate do with those disks? They remanufacture them and toss them back into the “refurbished” bin.
Although the disk has the capability to “remanufacture” itself in the firmware, it cannot be done inside your traditional array. The vibration is simply too high to do this reliably. A typical shelf full of rotating disks vibrates at over 40 rads (units of rotational vibration). When a dozen or more disks are all rotating at the same speed, in the same direction, it’s not hard to imagine the vibration in a tray of disks. Xiotech actually mounts its disks so that they are counter-rotating. One disk rotates clockwise, and the disk beside it is mounted so that the rotation is in the other direction. This reduces vibration inside the Xiotech box to 2 rads. This means they can reliably remanufacture a disk inside the box while the array is in operation.