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Re: debian-installer RAID question

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	Hi.

On Sat, Sep 11, 2021 at 06:55:56PM +0200, Felix Natter wrote:
> My question is: How does d-i know how the individual HDDs were combined
> into a RAID1?

mdraid stores its metadata on each drive that belongs to the RAID.
Whenever it's the beginning of the drive, or the end of it - depends on
mdraid metadata version - mdadm(8).

At least three things are stored on each drive:
- mdraid metadata version
- UUID of RAID array itself
- hostname that was used to create an array.

So, answering your question - d-i does not have to know all this.
It's kernel's job to detect your drives, and userspace's (mdadm) one to
search for mdraid metadata and assemble an appropriate array from the
detected drives.
RAID array assembly merely signals the kernel to consider a set of
drives an array.


tl;dr version. Each time you run "mdadm --detail --scan" all parts of
the result are taken from the metadata that's stored on each drive.


> The same thing applies when I boot a GNU/Linux rescue system: I think I
> can mount the RAID1 if I know the member partitions and type of RAID
> using mdadm?

The general answer is - you have to assemble (mdadm -A) your array
first. Before the assembly you have to know which arrays you have, hence
the need of "mdadm --detail --scan", or /etc/mdadm.conf.
Any rescue system worthy of its title should perform mdraid assembly for you.

Reco

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Thread

debian-installer RAID question Felix Natter <fnatter@gmx.net> - 2021-09-11 19:00 +0200
  Re: debian-installer RAID question Andy Smith <andy@strugglers.net> - 2021-09-11 19:10 +0200
    Re: debian-installer RAID question Felix Natter <fnatter@gmx.net> - 2021-09-18 12:00 +0200
  Re: debian-installer RAID question Reco <recoverym4n@enotuniq.net> - 2021-09-11 19:20 +0200
    Re: debian-installer RAID question Felix Natter <fnatter@gmx.net> - 2021-09-18 12:10 +0200
  Re: debian-installer RAID question Sven Hartge <sven@svenhartge.de> - 2021-09-11 19:30 +0200
    Re: debian-installer RAID question Felix Natter <fnatter@gmx.net> - 2021-09-18 12:00 +0200
  Re: debian-installer RAID question Andrei POPESCU <andreimpopescu@gmail.com> - 2021-09-12 12:20 +0200
    Re: debian-installer RAID question Felix Natter <fnatter@gmx.net> - 2021-09-18 11:50 +0200
  Re: debian-installer RAID question David Christensen <dpchrist@holgerdanske.com> - 2021-09-12 21:10 +0200
  Re: debian-installer RAID question Darac Marjal <mailinglist@darac.org.uk> - 2021-09-12 23:00 +0200
    Re: debian-installer RAID question Felix Natter <fnatter@gmx.net> - 2021-09-18 11:50 +0200

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