Re: RAID 6, 6 device array - all devices lost superblock

Eyal Lebedinsky
2022-08-29T22:38:53Z

On 30/08/2022 07.45, John Stoffel wrote:
>>>>>> "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

An aside, I would think the way to specify a list in a nominated order is something like

$ echo /dev/sd{c,d,a,b}
/dev/sdc /dev/sdd /dev/sda /dev/sdb

rather than

$ echo /dev/sd[cdab]
/dev/sda /dev/sdb /dev/sdc /dev/sdd

which will be in sorting order, regardless of the order of the letter.

--
Eyal Lebedinsky (fedora@eyal.emu.id.au)