Reopen: 16 HDDs too much for RAID6?

["Lars Täuber" <taeuber@bbaw.de>]

Hallo!

Lars Täuber <taeuber@bbaw.de> schrieb:
> I zeroed out all physical devices completely:
> # for DEV in /dev/sd[c-r]; do dd if=/dev/zero of=$DEV; done
> 
> Now the problem is gone. I don't know what really caused the problem.
> Many thanks for your suggestions.

The problem has occured again.
I'm not sure what the cause was, but the duplicated superblock is there again. But the raid fell apart before. So I suspect this occurs only after the array was degraded.
The discs are not defective so I tried to reassemble the array with the original discs again:
monosan:~ # mdadm -A /dev/md4
mdadm: WARNING /dev/dm-9 and /dev/dm-8 appear to have very similar superblocks.
      If they are really different, please --zero the superblock on one
      If they are the same or overlap, please remove one from the
      DEVICE list in mdadm.conf.

How can I extract the superblocks to check if they are really identically?

Thanks
Lars
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