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From:   Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
To:     Marc MERLIN <marc@merlins.org>
Cc:     Josef Bacik <josef@toxicpanda.com>,
        "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: Rebuilding 24TB Raid5 array (was btrfs corruption: parent
 transid verify failed + open_ctree failed)
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On Mon, Apr 04, 2022 at 06:42:59PM -0700, Marc MERLIN wrote:
> On Mon, Apr 04, 2022 at 09:22:26PM -0400, Josef Bacik wrote:
> > Ok lets try again with -b 13577821667328, and if the owner doesn't say
> > ROOT_TREE try 13577775284224 and then 13577814573056.  Thanks,
> 
> EXTENT_TREE, FS_TREE, and FS_TREE
> 
> And shit, I got distracted and sent the text output to
> /dev/mapper/dshelf1a, so I clobbered about 30K of the device. 
> I'm assuming there was probably something there?

First superblock is at 64K, and the first 1M of every device is unused.
A 30K write at the beginning will overwrite nothing important to btrfs.