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Wed, 28. Oct 2009


Works if you hotplug it Created: 28.10.2009 00:20
At work, there is this nice and rather new tape library. Said library had a defective gripper - that is the part with which it takes the tapes out of their slots and puts them into the tape drives, or the other way round. Why the gripper died is quite possibly a story for another posting, but todays subject is a different one:
The bad gripper was replaced last week, and for almost a week, the library worked flawlessly. Until Monday: The library stopped (again) and displayed an "Error 41A0", an error code on which google returned zero hits. So we called support, and they sent a technician and yet another gripper.
The technician tried to power cycle the library, with the effect that it didn't even get through all the normal power-up tests before displaying "Error 41A0" and stopping. So what is "Error 41A0"? The technician had the answer in his manuals: It means the gripper is incompatible with the library. Of course, that was complete nonsense - after all the library had been running for a week with that gripper before suddenly deciding it's an incompatible one.
So the gripper was replaced - again. The result however stayed the same - "Error 41A0".
It took three hours and numerous phone calls to find out what actually was the problem: The grippers, both the one from last week and the newest one, really were incompatible with our library. As it turns out, there are two types, the normal one, and one which has slightly stronger motors that it needs to be able to reliably put tapes into high density slots. Those are slots where not one but five tapes reside, packed one behind the other, so to get the last tape the gripper first has to pull out the four others sitting in front of it. Support sent us the normal model, but we have high density frames and thus need the stronger model.
 
So why had it worked for a week despite the gripper definitely being the wrong model? Well, almost everything in that library can be hotplugged, or at least semi-hotplugged. When the technician changed the gripper last week, he just told the library to turn off the gripper via software, then changed the gripper, then put the gripper online again via software. Apparrently, the library does not check if the gripper has been replaced with a different model in that situation. So it still saw the old gripper, and since apart from the motor strength they are actually the same, controlling the gripper worked just fine. It would have stayed that way until the next powercycle, if there hadn't been an "inventory" command. It obviously does check the gripper type when doing an inventory - and from that moment on there was no way of getting it to accept that wrong gripper again.
1 comment
Isn't this a little bit like "hotplugging" your girlfriend and then you notice after a while that it's the wrong one...?
RRZEschorscherl 30.10.2009 10:21

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