We are using a bar code scanner to scan the serial numbers of all hard disk drives we buy. This is supposed to make it easier and less error prone to put them into an Excel list for tracking their whereabouts (we use quite a lot of drives for storing video data).
Of course, when I bought 4 TB SATA drives for setting up yet another Linux server, I too put these drives in the list. And since I am a lazy bastard™ I borrowed the scanner to scan them. It worked like a charm so I returned the scanner and started building the raid.
I put labels on the drive bays with our internal number, so in the case of a drive failure I could use the list I mentioned to find out which drive to swap out.
One of the drives apparently was defective to start with, so what did I do? I asked mdadm which drive it was (/dev/sdg) and used
ls -l /dev/disk/by-id
to find its serial number.
lrwxrwxrwx 1 root root 9 Aug 14 08:59 ata-ST4000DM000-1F2168_Z301W61Y -> ../../sdg
Then I opened up the list to find the drive’s internal number. To my surprise, none of the serial numbers in the list seemed to match.
It turned out that on my computer, because I use a UK keyboard layout, the scanner swapped Y and Z. So, in the list the drive had the serial number Y301W61Z while in reality it was Z301W61Y.
Fun with computers, not.