Re: Device kicked from raid too easilly

["Stefan /*St0fF*/ Hübner" <stefan.huebner@stud.tu-ilmenau.de>]

Am 08.06.2010 07:15, schrieb Ian Dall:
> On Sat, 2010-06-05 at 09:22 +0200, Stefan /*St0fF*/ Hübner wrote:
> [...]
> 
> Puzzlingly, swapping the disks around in the backplane works so long as
> it is brand "A" in the first slot and not brand "B"! My current theory
> is that there are transmission line effects (or maybe RFI) which make
> some slots fall outside the range of the brand "B" disks to compensate!
> 
> One might think that sata would be better, but I am simultaneously
> looking for a problem in another raid array which gives me sata CRC
> errors which I assume to be cable related. Interestingly the sata
> transport layer treats these CRC errors as soft (at least, there is no
> corresponding action from md).

Weird, but on some Synology RackStations (RS407 and RS408) brand NAS
devices I had similar problems and what you wrote is exactly what I told
the customers what I think the problem might be.

The devices of mentioned make which failed, always failed slot #1.
Those that made problems, always kicked drive #1 sporadically.  But on
those problem-kids I could never find a real error.  Swapping another
disk into slot #1 made the problems disappear surprinsingly.  So I guess
you thoughts are right, some disks may be able to compensate
transmission-noise better than others.

But I wouldn't want to subject it to the cabling, because (well, I'm not
100% sure if that's right) slot #1's cable is the shortest.  I'd rather
think it might be not-so-well placed electronics on the board or
backplane.  Maybe a capacitor or a resistor (of which there should be
some for each port) are placed for port #1 that way, that they get a lot
warmer than the others ports' passive elements.  Resistors increase
resistance if they're hotter, capacitors loose capacity when they're
hotter.  So this might change the signal levels to some noticeable extent.

> 
>> P.S.: maybe you should check for firmware updates of the disks?
> 
> No such luck. These (brand "B") are "Worldisk" (which I believe to be
> re-manufactured Fujitsu). The less troublesome disks (brand "A") are
> Hitachi.

That's too bad.  But actually, if our shared thoughts above are right, a
firmware update wouldn't help much...
> 
> Thanks for your thoughts.
> 
> Regards,
> Ian
> 
Stefan
> [...]
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