Re: The "uniqueness" of UUIDs

From	Andy Smith <andy@strugglers.net>
Newsgroups	linux.debian.user
Subject	Re: The "uniqueness" of UUIDs
Date	2024-11-26 16:30 +0100
Message-ID	<JN5FM-bMw7-7@gated-at.bofh.it> (permalink)
References	<JMYXD-bIl2-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Hi,

On Tue, Nov 26, 2024 at 09:11:58AM +0100, Roger Price wrote:
> On Tue, 26 Nov 2024, George at Clug wrote:
> 
> > "$ lsblk -f" output is very nice !   Thanks.
> 
> I tried this and noticed UUID duplication in the output. I attach a small
> text file which shows what I saw. UUID sdg6 = UUID sdh6 !
> 
>  NAME    FSTYPE            UUID
>  ...
>  ├─sdg6  linux_raid_membe3 f5e37a29-357a-e3f2-c731-e29eddce5e
>  │ └─md3 ext4           1.039c24711-ab43-497c-bf3e-12b4032575a.4G
>  ...
>  ├─sdh6  linux_raid_membe3 f5e37a29-357a-e3f2-c731-e29eddce5e91
>  │ └─md3 ext4           39c39c24711-ab43-497c-bf3e-12b403257.4G
> 
> If I wanted to retire /dev/sdg6 from the Raid array, I would not be able to
> use the UUID, only the unique SDxn.
> 
> Aren't UUIDs supposed to be unique?

People see the phrase "UUID" and think every UUID is the same. Your
computer has lots of different UUIDs.

What you see above is the mdadm array UUID. It is meant to be unique PER
ARRAY (on that system). Those devices are part of the same array thus
they have the same ARRAY UUID. You don't have a filesystem on /dev/sdg6
or /dev/sdh6. If you did then it would have a FILESYSTEM UUID.

If you want to refer to sdg6 or sdh6 without using /dev/sd* then you can
use any of the /dev/disk/by-* paths for them.

See also the output of "mdadm --examine /dev/sdg6" and "mdadm --detail
/dev/md3".

Thanks,
Andy

-- 
https://bitfolk.com/ -- No-nonsense VPS hosting

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Thread

The "uniqueness" of UUIDs Roger Price <debian@rogerprice.org> - 2024-11-26 09:20 +0100
  Re: The "uniqueness" of UUIDs Hans <hans.ullrich@loop.de> - 2024-11-26 10:00 +0100
    Re: The "uniqueness" of UUIDs Roger Price <debian@rogerprice.org> - 2024-11-26 10:10 +0100
      Re: The "uniqueness" of UUIDs George at Clug <Clug@goproject.info> - 2024-11-26 10:40 +0100
  Re: The "uniqueness" of UUIDs Andy Smith <andy@strugglers.net> - 2024-11-26 16:30 +0100

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