Re: Reuniting disks in a raid1 array

From	Pascal Hambourg <pascal@plouf.fr.eu.org>
Newsgroups	linux.debian.user
Subject	Re: Reuniting disks in a raid1 array
Date	2016-08-30 20:20 +0200
Message-ID	<sbVND-8n7-21@gated-at.bofh.it> (permalink)
References	<sbJW9-BZ-1@gated-at.bofh.it> <sbOsO-3yX-41@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Le 30/08/2016 à 12:14, Mirko Parthey a écrit :
> On Tue, Aug 30, 2016 at 07:33:02AM +0200, Frédéric Marchal wrote:
>>
>> Do I have to wipe sdb before adding it to the new computer? If so, how do I
>> make sure raid data is gone from every one of the three partitions?
>
> The wipefs tool can remove RAID signatures.

Or mdadm --zero-superblock

> Deleting and recreating the partitions with the same size doesn't help
> on its own, because it will not affect the signatures.
> Overwriting the beginning of the disk or the partitions may not be
> sufficient either, because depending on the RAID superblock version, it
> might be stored at the end.

The default superblock format 1.2 stores the superblock 4 KiB after the 
beginning. However the OP wrote the disk was divided in several RAID 
partitions, so it would not erase all the superblocks.

>> Or maybe mdadm will see that sda was used more recently than sdb and will
>> synchronize sda onto sdb?
>
> I would advise against such experiments. It's best to wipe the signatures
> while the disk is still in the old computer, then transfer it to the new
> one.

I second this advice.

> A bootable rescue system such as GRML can be very handy for this job.

Or you can just use the initramfs shell. Add "break" to the kernel 
command line to trigger it. Or the Debian installer shell.

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Reuniting disks in a raid1 array Frédéric Marchal <frederic.marchal@wowtechnology.com> - 2016-08-30 07:40 +0200
  Re: Reuniting disks in a raid1 array Lars Noodén <lars.nooden@gmail.com> - 2016-08-30 10:40 +0200
    Re: Reuniting disks in a raid1 array Lars Noodén <lars.nooden@gmail.com> - 2016-08-30 10:50 +0200
    Re: Reuniting disks in a raid1 array Frédéric Marchal <frederic.marchal@wowtechnology.com> - 2016-08-30 11:10 +0200
  Re: Reuniting disks in a raid1 array Mirko Parthey <mirko.parthey@web.de> - 2016-08-30 12:30 +0200
    Re: Reuniting disks in a raid1 array Pascal Hambourg <pascal@plouf.fr.eu.org> - 2016-08-30 20:20 +0200

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