>>105783873
It's the same as the older one.
>can a MAC address tell us anything?
No, only the vendor.
>are there patterns of first few digits reserved for certain manufacturers or anything like that?
First half tells the vendor, the rest is a running number.

>>105783405
Are we talking about HDDs specifically? No, your typical external HDD is basically just picrel, but with a plastic case -> a SATA to USB converter.
External SSDs on the other hand vary hugely.