[...] > I was referring to what fdisk -l calls "disk > identifier". [...] That's not a very fruitful approach :-). The real disk identifiers are the serial number or WWN. What 'fdisk' reports is the identifier of the "label" (called by 'fdisk' "Disklabel", which is a metadata block which usually contains the partition table, and of which there are several types). For MBR/DOS type labels that is a pretty obscure field at offset 0x1B8 on the disk, and it is a 32b field. I personally use it to store 4 characters, but it can be any 32-bit value. That value matters a lot more to MS-Windows than to GNU/Linux, which basically ignores it. I find that value used under '/dev/disk/by-partuuid/' where it is used to prefix the number of the partition for DOS/MBR labeled disks. BTW the entries under '/dev/disk/' seem to me a "legacy" mess. GPT/EFI labels instead have 128b fields which are usually filled with UUID-structured random values, and those are not ignored and usually appear under '/dev/disk/by-uuid'. For MD raid sets I like to use GPT labels and refer to RAID set members by partition name, where I give those partitions meaningful proper-name prefixes. But that's another story.
