On 30/09/2021 18:21, Clemens Kiehas wrote:
Hello,
until recently I was using Unraid with 8 disks in an XFS array.
I installed Debian on a spare SSD on the same machine and started
migrating disk by disk from the Unraid array to a raid5 array using a
second server as temporay storage. So I switched between Debian and
Unraid a lot to copy data and remove/add drives from/to arrays.
From the beginning I always had to assemble the array without /dev/sdd,
add it afterwards and let it rebuild - since the array was working fine
afterwards I didn't really think much of it.
Not wise - as you've found out it was trashing your redundancy ...
Appearently Unraid always overwrote the superblock of that 1 (and later
2) disks (/dev/sdc and /dev/sdd) when I switched between the two OSs and
now mdadm isn't recognizing those 2 disks and I can't assemble the array
obviously.
At least that's what I think happened, since file tells me that the
first 32k bytes are XFS:
# losetup -o 32768 -f /dev/sdd
# file -s /dev/loop0
/dev/loop0: SGI XFS filesystem data (blksz 4096, inosz 512, v2 dirs)
That feels good, but I'm not sure how to proceed from here.
Right now mdadm only assembles 5 (instead of 7) disks as spares into an
inactive array at boot:
# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
[raid4] [raid10]
md0 : inactive sde[6](S) sdf1[5](S) sdg[1](S) sdh[3](S) sdi[8](S)
21487980896 blocks super 1.2
unused devices: <none>
My system:
Linux titan 5.10.0-8-amd64 #1 SMP Debian 5.10.46-4 (2021-08-03) x86_64
GNU/Linux
mdadm - v4.1 - 2018-10-01
Maybe I could try to assemble it with assume-clean and read-only?
I found some pages in the wiki but I'm not 100% sure that they will
solve my problem and I don't want to make things worse.
https://raid.wiki.kernel.org/index.php/Recovering_a_damaged_RAID
https://raid.wiki.kernel.org/index.php/RAID_Recovery
The first page talks about overlays. THEY WILL PROTECT YOUR DATA.
Make sure every disk is overlayed, then try assembling the overlays with
your assume-clean. You won't need read-only but do it if you like it
then do.
If you can then mount and run a fsck or whatever it is over the file
system and it says everything is clean, then you can redo it without the
overlays and recover the array properly. If it's messed up, just tear
down the overlays and you're back where you started.
If it doesn't work, come back and tell us what happened (if it does
work, please let us know :-)
Cheers,
Wol
