Why do disk UUIDs have a few variants of form?

Question

Here are some of my hard disk UUIDs

/dev/disk/by-uuid/B0EA1359EA131B64                     -> ../../sda1
/dev/disk/by-uuid/C814-23EC                            -> ../../sda2
/dev/disk/by-uuid/6A1016BD10169065                     -> ../../sda4
/dev/disk/by-uuid/e1e5f4ec-094f-4cf1-b0a6-4ed7a0498b25 -> ../../sda5
/dev/disk/by-uuid/86e26b30-af5a-47a9-a57d-cddf785e1979 -> ../../sda7
/dev/disk/by-uuid/5DC0908E72D3BB2A                     -> ../../sdb2
/dev/disk/by-uuid/760630a7-223f-42e4-aecf-de92e32f12b9 -> ../../sdb3

These forms are semi-regular. Some have 17 characters uppercase, some have 33 character lowercase plus four hyphens, one has 4-4.

I can't see any rhyme or reason as to why some have one form and some another. What is the scheme which decides this?

Answer 1

It depends on the filesystem on your partition. UUID in 4-4 format is normally FAT, 17 characters are NTFS and all other filesystems should use the standard UUID format.