Re: BTRFS messes up snapshot LV with origin

[Robert White <rwhite@pobox.com>]

On 11/28/2014 11:29 PM, Duncan wrote:
> Since I can't/won't run pretty much anything proprietary, there's little
> chance of it being taken as anything but Linux, here.  (Tho I actually
> use (c)gdisk for partitioning here and it appears to use a different GUID.
> (0700 in its short form which AFAIK is gdisk specific, for MS basic data,
> while it uses 8300 for general Linux filesystems.  I could look up the
> long form GUIDs, but meh...)

Partition type codes (e.g. 0700, 8300, EF00, etc) have _nothing_ to do 
with UUIDs. They are type codes. They aren't "short form" of anything 
else at all. In fact 0700 is the _long_ _form_ of the original code of 
"7", but in big-endian order now that it went from one byte to two.

Microsoft started using pre-assigned UUIDs as "classes", e.g. type codes 
they could cram into their various registry files. If you actually read 
the registry you'll find a lot of places where "rational word" is 
defined as {some_uuid_here} and then eslwere {some_uuid_here} has a 
bunch of data items attached to it.

So gpartd didn;t "reuse" microsoft UUIDs.

In some/many of the older formats there was a code for "operating system 
data" (which I think is what 7 was originally). Others came by and said 
"since we're going to put in a type code for "linux swap" (82) then lets 
put in a code for linux data as well (83), and all this before the whole 
byte expansion to turn these things from bytes into two-byte words.

Once everybody else picked their own type codes for their data 
partitions, everybody just started calling "7" microsoft data. And linux 
doesn't care at all since it's noise since every partition just ends up 
as /dev/[sh]d? anyway.

All this stuff has historical reasons. GNU/Linux attempts to be an 
egalitarian actor so it adapts to whatever you do.