Why you should never completely trust commercial products. (OR, never trust past employees of your company)

So, I brought home a scsi drive array from work that was sitting idle with 18G. It was at our colocation center and just sitting in a corner. My boss said I could have it. Yahoo! Free hardware.

That is, until I found "it didn't work." I've spent the last week or two tinkering, fiddling, figuring out if the problems with the drive array were with the card, the cables, the drives, or the case. If I had the drives in certain combinations, the array would partially work. If I had the drives in other slots, the whole thing would produce a loud shriek from my adaptec raid card.

Finally I was so annoyed by this problem that I popped open the case to the array and took a look inside. I was expecting to see resistors for drive ID's and thinking it must be a lost cause to tinker. Much to my happiness, I found that there were indeed jumpers for the scsi ID. What I wasn't prepared for was the configuration thereof.

For those who are not aware, scsi ID's are based on the binary code for 0 through 15. It works something like this:

0000 - SCSI ID 0
0001 - SCSI ID 1
0010 - SCSI ID 2
0011 - SCSI ID 3

And so on and so forth.

You'd expect that the manufacturer of the drive array would realize this to be the case. However, what greeted me was some very interesting math. It appeared that whoever set up the jumpers set them up to use 0,1,2,3 as decimal math as opposed to binary math. So, it was a creatively odd hodgepodge of scsi ID's in the case. I think they would have been able to pull it off, too, except for the fact that one of the scsi slots had real scsi ID 7, (0111, or 2+1+0).

That was the holy shitstorm my scsi card was raising. One of the freaking drive slots had scsi ID 7! For those not in the know, scsi ID 7 is traditionally the ID of the scsi card. When things collide on the SCSI bus with the adapter, weird things happen, (like the card spitting out that it had 32 IBM drives in it when it could only physically have 15).

Anyway, a simple bit of tweezers maintenance and the drive array is good-as-new, and is now rebuilding it's 8-disk RAID5 in preparation for me to migrate my Xen install to vmware.

Yahoo!
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NOTE: Frank brought to my attention that it probably wasn't the factory, but the previous people who worked at my company who did this little feat of brilliance. Upon further investigation, the fact that the jumpers are of differing designs lends a great deal of credibility to that assumption. Therefore, Sorry <People Who Made Random Unlabeled Drive Array>, it really wasn't your people who were stupid.