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Date:   Mon, 29 Aug 2022 17:45:43 -0400
From:   "John Stoffel" <john@stoffel.org>
To:     Peter Sanders <plsander@gmail.com>
Cc:     John Stoffel <john@stoffel.org>, Phil Turmel <philip@turmel.org>,
        Wols Lists <antlists@youngman.org.uk>,
        NeilBrown <neilb@suse.com>, linux-raid@vger.kernel.org
Subject: Re: RAID 6, 6 device array - all devices lost superblock
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>>>>> "Peter" == Peter Sanders <plsander@gmail.com> writes:

Peter> Phil,
Peter> fstab from the working config -

Peter> # <file system> <mount point>   <type>  <options>       <dump>  <pass>
Peter> # / was on /dev/sda1 during installation
Peter> UUID=50976432-b750-4809-80ac-3bbdd2773163 /               ext4
Peter> errors=remount-ro 0       1
Peter> # /home was on /dev/sda6 during installation
Peter> UUID=eb93a2c4-0190-41fa-a41d-7a5966c6bc47 /home           ext4
Peter> defaults        0       2
Peter> # /var was on /dev/sda5 during installation
Peter> UUID=d1aa6d1f-3ee9-48a8-9350-b15149f738c4 /var            ext4
Peter> defaults        0       2
Peter> /dev/sr0        /media/cdrom0   udf,iso9660 user,noauto     0       0
Peter> /dev/sr1        /media/cdrom1   udf,iso9660 user,noauto     0       0
Peter> # raid array
Peter> /dev/md0    /mnt/raid6    ext4    defaults    0    2

Peter> No LVM, one large EXT4 partition

Peter> I have several large files ( NEF and various mpg files) I can identify
Peter> and have backup copies available.

Peter> I have the overlays created. 300G for each of the six drives.

So that's good.  Now you have to try and figure out which order they
were created in.  As the docs show, you setup the overlayfs on top of
each of the six drives.  

Keep track by noting the drive serial numbers, since Linux can move
them around and change drive letters on reboots.


Then using the overlays, do an:

     mdadm --create /dev/md0 --level=raid6 -n 6 /dev/sd[bcdefg] 
     fsck -n /dev/md0

and see what you get.  If it doesn't look like a real filesystem, then
you can break it down, and then modify the order you give the drive
letters, like:

	 /dev/sd[cdefge]

and rinse and repeat as it goes.  Not fun... but should hopefully fix
things for you.

John